Method for depositing a composite coating on the surface of a titanium-aluminum alloy

Abstract

The application provides a method for depositing a coating on a titanium-aluminum alloy surface, and belongs to the technical field of alloy coating preparation. The method comprises the following steps: subjecting the titanium-aluminum alloy to at least two times of melting treatment to obtain a sample to be treated; taking a graphite plate as an anode, taking the sample to be treated as a cathode, and connecting the sample to be treated and the graphite plate through an electrolyte; wherein the electrolyte is an Al(NO3)3 and Y(NO3)3 solution or an Al(NO3)3 and Ni(NO3)2 solution; and depositing a composite coating on the titanium-aluminum alloy surface through a cathode plasma electrolytic deposition process. The cathode plasma electrolytic deposition technology is used to form the composite coating on the titanium-aluminum alloy surface, the preparation process is simple, the time consumption is short, the high-temperature oxidation resistance of the material can be significantly improved, and the components and contents of the composite coating can be effectively controlled.

Description

Technical Field

[0001] This invention belongs to the field of alloy coating preparation technology, and specifically relates to a method for depositing a composite coating on the surface of titanium-aluminum alloys. Background Technology

[0002] TiAl intermetallic compounds, possessing low density, high specific strength, and high melting point, combined with the advantages of both ceramics and metals, hold promise for replacing traditional nickel-based superalloys in aero-engine applications within the medium temperature and stress range to achieve weight reduction. However, their insufficient high-temperature oxidation resistance limits their application, which has become an urgent requirement for the engineering application of these alloys. Nevertheless, surface treatment of TiAl alloys can improve their high-temperature oxidation resistance without significantly altering their mechanical properties.

[0003] Currently, there are methods to improve the oxidation resistance of titanium-aluminum alloys by preparing Al-Si coatings through silicon infiltration. Studies have found that Si can combine with Ti, reducing the activity of Ti and relatively increasing the activity of Al in the coating. Moreover, the relative content of Al in the coating is also significantly increased, resulting in the formation of a dense Al2O3 film on the surface, thereby improving the oxidation resistance of titanium-aluminum alloys. However, since the coating is a single aluminide coating, although it has a certain positive effect on the oxidation resistance of titanium-aluminum alloys, it also has obvious defects. Among them, due to the difference in composition between the coating and the substrate, element interdiffusion will occur, which will lead to premature failure of the coating in high-temperature environments.

[0004] Secondly, existing technologies also include adding materials to the surface coating of the mold shell, so that after the molten TiAl alloy melt is poured into the mold shell, the added materials in the surface coating react and diffuse appropriately with the TiAl alloy melt to form a protective layer on the surface of the TiAl alloy casting. This method is time-consuming and the preparation process is complicated.

[0005] Furthermore, existing technologies also employ a combined process of arc ion plating to deposit Cr and powder embedding to infiltrate Al to prepare an Al-Cr coating on the surface of a nickel-based superalloy DSM11 substrate, which significantly improves the high-temperature oxidation resistance of the substrate alloy. However, this method uses micro-arc oxidation technology, which cannot accurately control the Al and Cr content in the coating, increasing the difficulty of preparation. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art, and provides a method for depositing composite coatings on the surface of titanium-aluminum alloys, so as to solve the problems of long time consumption, complex preparation process, difficulty in controlling the element content in the coating and poor high-temperature oxidation resistance.

[0007] This invention proposes a method for depositing composite coatings on the surface of titanium-aluminum alloys.

[0008] The methods include:

[0009] The titanium-aluminum alloy was subjected to at least two melting processes as samples to be processed;

[0010] A graphite plate is used as the anode, and the sample to be treated is used as the cathode. The sample to be treated is connected to the graphite plate through an electrolyte. The electrolyte is an Al(NO3)3 and Y(NO3)3 solution or an Al(NO3)3 and Ni(NO3)2 solution.

[0011] A composite coating is deposited on the surface of the titanium-aluminum alloy using a cathode plasma electrolytic deposition process.

[0012] Optionally, when the electrolyte is an Al(NO3)3 and Y(NO3)3 solution, an Al2O3-Y2O3 composite coating is deposited on the surface of the titanium-aluminum alloy by a cathode plasma electrolytic deposition process, wherein the composite coating contains a porous structure.

[0013] Optionally, the thickness of the Al2O3-Y2O3 composite coating ranges from 23.01 μm to...

[0014] 24.04μm.

[0015] Optionally, the molar concentration ratio of Y(NO3)3 to Al(NO3)3 in the Al(NO3)3 and Y(NO3)3 solution is 1:(19-21).

[0016] Optionally, when the electrolyte is an anhydrous ethanol solution of Al(NO3)3 and Ni(NO3)2, an Al2O3-Ni composite coating is deposited on the surface of the titanium-aluminum alloy by a cathode plasma electrolytic deposition process, and Ni is deposited in the porous structure of the composite coating.

[0017] Optionally, the thickness of the Al2O3-Ni composite coating ranges from 18 μm to 21 μm.

[0018] Optionally, the molar concentration ratio of Al(NO3)3 to Ni(NO3)2 in the Al(NO3)3 and Ni(NO3)2 solution is (4-6):1.

[0019] Optionally, the electrolyte may be an aqueous solution and / or a low surface tension organic solvent.

[0020] Optionally, when the solvent used in the electrolyte is an aqueous solution, the deposition voltage of the cathode plasma electrolytic deposition process is 180V to 220V, the deposition time is 500s to 700s, and the duty cycle is 70% to 90%; or,

[0021] When the electrolyte is a low-surface-tension organic solvent, the deposition voltage of the cathode plasma electrolytic deposition process is 110V to 150V, the deposition time is 50s to 70s, and the duty cycle is 50% to 70%.

[0022] Optionally, the titanium-aluminum alloy is Ti-45Al-8.5Nb.

[0023] This invention proposes a method for depositing a coating on the surface of a titanium-aluminum alloy. The method includes: subjecting the titanium-aluminum alloy to at least two melting processes as a sample to be treated; using a graphite plate as the anode and the sample to be treated as the cathode, with the sample to be treated connected to the graphite plate via an electrolyte; wherein the electrolyte is an Al(NO3)3 and Y(NO3)3 solution, or an Al(NO3)3 and Ni(NO3)2 solution; and depositing a composite coating on the surface of the titanium-aluminum alloy using a cathode plasma electrolytic deposition process. This invention uses cathode plasma electrolytic deposition technology to form a composite coating on the surface of a titanium-aluminum alloy. The preparation process is simple and time-saving, while significantly improving the high-temperature oxidation resistance of the material and effectively controlling the elemental content of the coating. Attached Figure Description

[0024] Figure 1 This is a flowchart of a method for depositing a composite coating on a titanium-aluminum alloy surface according to an embodiment of the present invention.

[0025] Figure 2 The surface and cross-sectional morphology of the Al2O3-Y2O3 composite coating in Example 1 of this invention are shown; wherein, Figure 2 (a) in the figure represents the surface morphology; Figure 2 (b) in the figure represents the cross-sectional morphology;

[0026] Figure 3 The oxidation weight gain curve of the titanium-aluminum alloy with Al2O3-Y2O3 composite coating in Example 1 of the present invention after high-temperature oxidation at 900℃ for 100h is shown.

[0027] Figure 4 The surface morphology of the titanium-aluminum alloy with Al2O3-Y2O3 composite coating in Example 1 of the present invention after high-temperature oxidation at 900°C for 100 hours.

[0028] Figure 5 The surface morphology of Ti-45Al-8.5Nb after high-temperature oxidation at 900℃ for 100h in Examples 1 and 2 of this invention;

[0029] Figure 6 The surface morphology of the titanium-aluminum alloy with Al2O3 coating in Examples 1 and 2 of the present invention after high-temperature oxidation at 900°C for 100 hours is shown.

[0030] Figure 7The surface and cross-sectional morphology of the Al2O3-Ni composite coating in Example 2 of the present invention are shown; wherein, Figure 7 (a) in the figure represents the surface morphology; Figure 7 (b) in the figure represents the cross-sectional morphology;

[0031] Figure 8 The oxidation weight gain curve of the titanium-aluminum alloy with Al2O3-Ni composite coating in Example 2 of the present invention after high-temperature oxidation at 900℃ for 100h is shown.

[0032] Figure 9 The surface morphology of the titanium-aluminum alloy with Al2O3-Ni composite coating in Example 2 of the present invention after high-temperature oxidation at 900℃ for 100h is shown. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0034] Unless otherwise specifically stated, the technical or scientific terms used in this invention should be understood in their ordinary sense by one of ordinary skill in the art to which this invention pertains. The terms "comprising" or "including," as used in this invention, do not limit the shapes, numbers, steps, and / or groups thereof mentioned, nor do they exclude the appearance or inclusion of one or more other different shapes, numbers, steps, and / or groups thereof.

[0035] like Figure 1 As shown, the present invention proposes a method S100 for depositing a coating on the surface of a titanium-aluminum alloy, comprising steps S110 to S130:

[0036] S110. The titanium-aluminum alloy is subjected to at least two melting processes and formed into a cylindrical sample to be processed.

[0037] Specifically, the titanium-aluminum alloy was melted into ingots using a magnetic levitation melting furnace under an Ar atmosphere. To ensure uniform composition and reduce Nb segregation, the ingots underwent at least two melting processes. Afterward, the melted ingots were cut into cylindrical samples, and each surface of the samples was polished with SiC and ultrasonically cleaned with anhydrous ethanol for 3 minutes.

[0038] After 6 minutes of cleaning, the sample is dried for later use.

[0039] Furthermore, the titanium-aluminum alloy in this embodiment uses a Ti-45Al-8.5Nb alloy matrix. Of course, it is not limited to the above-mentioned titanium-aluminum alloy; the method of this embodiment can also be used with Cr-Al2O3, FeAl alloys, NiAl alloys, etc.

[0040] S120. A graphite plate is used as the anode and the sample to be treated is used as the cathode. The sample to be treated is connected to the graphite plate through an electrolyte. The electrolyte is an Al(NO3)3 and Y(NO3)3 solution or an Al(NO3)3 and Ni(NO3)2 solution.

[0041] Specifically, in this embodiment, a quartz electrolytic cell is used, with two parallel graphite plates as the anode and the sample to be processed formed in step S110 as the cathode, which is placed at the center of the graphite electrode. The electrolyte is placed in the electrolytic cell to connect the cathode and the anode through the electrolyte.

[0042] It should be noted that this embodiment does not specifically limit the solvent of the electrolyte. It can be an aqueous solution or a low surface tension organic solvent, such as methanol, ethanol, or a mixture of methanol and ethanol. Of course, other low surface tension organic solvents can also be selected.

[0043] For example, the electrolyte can be an aqueous solution of Al(NO3)3 and Y(NO3)3, an aqueous solution of Al(NO3)3 and Y(NO3)3 in ethanol, an aqueous solution of Al(NO3)3 and Ni(NO3)2, an aqueous solution of Al(NO3)3 and Ni(NO3)2 in ethanol, an aqueous solution of Al(NO3)3 and Ni(NO3)2 in ethanol, an aqueous solution of Al(NO3)3 and Ni(NO3)2 in methanol, etc.

[0044] It should be further noted that while anhydrous ethanol can dissolve metal nitrates using it as a solvent, its lower conductivity results in a higher critical arc-starting voltage compared to aqueous solutions, leading to a longer deposition time. Furthermore, the low surface tension of organic solvents like ethanol necessitates a larger critical bubble size, resulting in a more moderate plasma discharge in the system during step S130, which significantly reduces thermal stress and prevents cracking of the coating.

[0045] It should be understood that, considering both cost and practical needs, the solvent for the electrolyte can be a mixture of ethanol and water.

[0046] S130, a composite coating is deposited on the surface of titanium-aluminum alloy by cathode plasma electrolytic deposition process.

[0047] Specifically, an electrolyte solution is prepared and poured into a quartz electrolytic cell. The cleaned sample to be treated is clamped on the cathode connection device, and the graphite plate is clamped on the anode connection device. The power is turned on and set to AC power mode. Parameters such as voltage, current, duty cycle, and frequency are set. After the time is up, the power is turned off, the sample is taken out, and ultrasonically cleaned with anhydrous ethanol or water. It is then dried to obtain a titanium-aluminum alloy with a composite coating.

[0048] It should be noted that the cathode electrolytic plasma technology used in this embodiment involves significant changes in the electrode process compared to conventional electroplating. For example, the electrode process changes from the double-layer theory to the triple-layer theory. Therefore, the solution composition, electroplating parameters, and electrode processes of conventional plating processes are no longer applicable to cathode electrolytic plasma deposition. This necessitates the analysis of various parameters and solution composition in the preparation process.

[0049] Specifically, when the electrolyte is an aqueous solution of Al(NO3)3 and Y(NO3)3, the deposition voltage range is 110V to 150V, the duty cycle range is 50% to 70%, and the deposition time range is 50s to 70s. The resulting composite coating is an Al2O3-Y2O3 composite coating with a thickness of 23μm to 24.04μm.

[0050] In the aqueous solution of Al(NO3)3 and Y(NO3)3, the molar concentration ratio of Al(NO3)3 to Y(NO3)3 is (19-21):1, for example, 20:1.

[0051] In some preferred embodiments, the deposition voltage is 130V, the duty cycle is 60%, and the reaction time is 60s.

[0052] This embodiment generates continuous and stable electrolytic plasma only within the above-mentioned deposition parameter range, which helps to deposit the coating and thus improves the high-temperature oxidation resistance of the alloy substrate.

[0053] Among them, as the deposition time increases, the thickness of the composite coating first increases and then decreases. At the same time, as the deposition time increases, the surface roughness of the composite coating decreases. Therefore, the optimal deposition time is 60s.

[0054] Secondly, with the increase of deposition voltage, both the thickness and surface roughness of the composite coating showed an increasing trend, indicating that the deposition conditions that maximized the thickness of the composite coating also maximized the surface roughness. Simultaneously, with the increase of deposition voltage, the oxidation weight gain of the sample first decreased and then increased, indicating that the high-temperature oxidation resistance of the sample first improved and then decreased. Therefore, the optimal deposition voltage is 130V.

[0055] In addition, as the duty cycle increases, the thickness and surface roughness of the composite coating both show a trend of first increasing and then decreasing. At the same time, as the duty cycle increases, the high-temperature oxidation resistance of the sample also shows a trend of first increasing and then decreasing. Furthermore, the bonding strength between the composite coating and the substrate also shows a trend of first increasing and then decreasing as the duty cycle increases. Therefore, the optimal duty cycle is 60%.

[0056] Specifically, the composite coating deposition process is as follows: During the reaction process, cations (Al) 3+ Y 3+ H + Under the influence of the electric field, the electrolyte migrates towards the cathode surface. Due to the activity series of metals, the hydrogen evolution reaction occurs first at the cathode electrode surface, leaving a large amount of OH- in the electrolyte. - Ions. Hydrogen gas is adsorbed on the cathode surface, forming a hydrogen film layer. Al 3 + Y 3+ Ions react with a large amount of OH- in the electrolyte. - When ions combine to form colloids, a pronounced Tyndall effect can be observed. These colloids adsorb excess Al from the electrolyte. 3+ Y 3+ Ions cause the colloidal particles to become positively charged, continuing their migration towards the cathode surface. As the deposition voltage increases further, the hydrogen evolution rate at the cathode surface is much greater than the rate at which hydrogen escapes from the electrolyte system. The cathode surface remains covered by a hydrogen film, and with increasing deposition time, the bubble size increases, leading to a decrease in the distance between the cathode and anode, and a rapid increase in the electric field strength E. This reaches the critical breakdown field strength E. c At this point, hydrogen bubbles on the cathode surface are broken down, forming a continuous and stable discharge plasma. The breakdown of hydrogen bubbles on the cathode surface allows colloids to reach the cathode surface. The energy from the breakdown and bursting of the bubbles decomposes the colloids into Al₂O₃ and Y₂O₃, which are then deposited on the cathode surface. The breakdown of hydrogen bubbles always occurs in relatively thin areas of the coating; therefore, coating continues to deposit in these thinner areas, making the entire coating appear continuous and dense.

[0057] This embodiment employs cathode electrolytic plasma technology. When the voltage exceeds a certain critical value, the gas film and oxide film generated on the cathode surface will be broken down to generate discharge, thereby forming electrolytic plasma. This allows for the deposition of coatings on metal or alloy surfaces of any shape. In other words, this invention obtains a continuous and dense composite coating by repeatedly electrolytically breaking down liquid-phase plasma in relatively weak areas of the coating, thus solving the problem of micro-arc oxidation technology being limited by valve metals and their alloys.

[0058] The composite coating formed in this embodiment has a good bond with the titanium-aluminum alloy substrate and no obvious cracks or pores. Compared with the titanium-aluminum alloy substrate, the high-temperature oxidation resistance of the titanium-aluminum alloy with Al2O3-Y2O3 composite coating is improved. Although the coating is a ceramic layer with a porous structure, it has fewer surface cracks and better high-temperature oxidation resistance than a single alumina coating. The preparation process is short, and the composite coating can be deposited on the surface of the titanium-aluminum alloy in just 60 seconds.

[0059] Specifically, in some preferred embodiments, when the electrolyte is an anhydrous ethanol solution of Al(NO3)3 and Ni(NO3)2, a composite coating is deposited on the surface of the titanium-aluminum alloy by a cathode plasma electrolytic deposition process. In this composite coating, Ni is deposited in the pore structure of the composite coating. That is to say, the formed composite coating is an Al2O3-Ni composite coating. This composite coating does not have a porous structure, which greatly improves the high-temperature oxidation resistance of the titanium-aluminum alloy.

[0060] The thickness of the Al2O3-Ni composite coating ranges from 18 μm to 21 μm. The molar concentration ratio of Al(NO3)3 to Y(NO3)3 in the anhydrous ethanol solution of Al(NO3)3 and Ni(NO3)2 is (4–6):1.

[0061] Furthermore, when the electrolyte is an anhydrous ethanol solution of Al(NO3)3 and Ni(NO3)2, the deposition voltage range of the cathode plasma electrolytic deposition process is 180V to 220V, the deposition time range is 500s to 700s, and the duty cycle range is 70% to 90%.

[0062] In some preferred embodiments, the deposition voltage is 200V, the duty cycle is 80%, and the deposition time is 600s.

[0063] This embodiment generates continuous and stable electrolytic plasma only within the above-mentioned deposition parameter range, which helps to deposit composite coatings and thus improves the high-temperature oxidation resistance of the titanium-aluminum alloy substrate.

[0064] It should be noted that, since anhydrous ethanol was chosen as the solvent in this embodiment, which has a lower conductivity, the critical arc initiation voltage is about 100V higher than that in aqueous solution. The deposition voltage selected in the experiment was about 200V. The current density during deposition is 1 / 10 of that in the aqueous solution system. Therefore, the deposition time was extended by 10 times to ensure that the amount of electricity Q flowing through the deposition process remained consistent.

[0065] In this embodiment, the Al2O3-Ni composite coating exhibits good adhesion to the titanium-aluminum alloy substrate, with no obvious cracks or pores. Analysis of the 900℃ air-circulating oxidation curve shows no significant cracking at 900℃, indicating that its application temperature is above 900℃. This demonstrates that Ni is deposited within the porous structure of the Al2O3 ceramic, forming the Al2O3-Ni composite coating. This composite coating significantly reduces the number and size of pores on the coating surface, thereby significantly improving the high-temperature oxidation resistance of the alloy material.

[0066] In this embodiment, the phase of the composite coating can be controlled by controlling the reaction conditions, so that the composite coating has a definite composition and content.

[0067] The following will further illustrate the method for depositing composite coatings on titanium-aluminum alloy surfaces with reference to several specific embodiments:

[0068] Example 1

[0069] The method for depositing a composite coating on a titanium-aluminum alloy surface in this example includes the following steps:

[0070] S1. Cut the Ti-45Al-8.5Nb ingot into Φ6×80mm round rods. Polish each side of the sample with SiC sandpaper and ultrasonically clean it with anhydrous ethanol for 5 minutes. After cleaning, dry the sample for later use.

[0071] S2. A WWL-PS DC regulated switching power supply is used. The electrolytic cell is a quartz glass container. The anode is connected to parallel sheet graphite plates. The sample to be processed, Ti-45Al-8.5Nb alloy substrate, is used as the cathode and placed at the center of the graphite electrode.

[0072] S3. Prepare an aqueous solution of Al(NO3)3 and Y(NO3)3, wherein the molar concentration ratio of the two is 20:1, and the Al(NO3)3 concentration is 1 mol / L. Pour the electrolyte into a quartz electrolytic cell. The cleaned sample is clamped on the cathode connection device, and the graphite sheet is clamped on the anode connection device. Turn on the power supply, set it to AC power mode, and set the deposition process parameters as follows: 130V deposition voltage, 60% deposition duty cycle, and 60s deposition time. After the deposition time is up, turn off the power supply, remove the sample, and ultrasonically clean it with anhydrous ethanol, then dry it with a hair dryer.

[0073] like Figure 2 As shown, the surface and cross-sectional morphology of the deposited Al2O3+Y2O3 composite coating are presented, wherein, according to Figure 2 As shown in (a), the composite coating has a porous structure on its surface, and the surface coating is relatively complete and can fully cover the coating surface.

[0074] like Figure 2As shown in (b), the coating is well bonded to the substrate and there are no obvious cracks or holes. In the coating area, the porous structure inside the particles can be seen. The average thickness of the coating is 24.04 μm, which can effectively improve corrosion resistance and high-temperature oxidation resistance.

[0075] like Figure 3 The high-temperature oxidation resistance of the deposited Al2O3+Y2O3 composite coating is shown in the figure. The weight gain of the composite coating after 100 hours of oxidation is 0.88 mg / cm³. 2 Less than 0.94 mg / cm³ of the Ti-45Al-8.5Nb alloy matrix. 2 .

[0076] like Figure 4 As shown, the surface morphology characterization results of the composite coating after 100h high-temperature oxidation are presented. The exposed area in the middle is a mixed oxide of Al2O3 and TiO2, and the needle-like Al2O3 particles and blocky TiO2 particles are significantly reduced.

[0077] Combined Figure 5 As shown, after 100 hours of thermal oxidation, the surface of an untreated Ti-45Al-8.5Nb alloy substrate mainly consists of needle-like Al2O3 particles and blocky TiO2 particles, with the TiO2 content significantly exceeding the Al2O3 content. This is because γ-TiAl cannot undergo selective preferential oxidation of Al; the diffusion rate of Ti in TiO2 is much greater than that of Al in Al2O3, resulting in more rapid TiO2 growth and a higher TiO2 content on the oxidized surface. Figure 6 As shown, an Al2O3 coating was deposited on the surface of a Ti-45Al-8.5Nb alloy substrate. After 100 hours of high-temperature oxidation, a small amount of needle-like Al2O3 particles and blocky TiO2 particles still existed on the surface of the coating.

[0078] In summary, the Al2O3+Y2O3 composite coating formed on the Ti-45Al-8.5Nb surface using Al(NO3)3 and Y(NO3)3 aqueous solutions as electrolytes exhibits better high-temperature oxidation resistance than the single Al2O3 coating formed on the titanium-aluminum alloy surface.

[0079] Example 2

[0080] The method for depositing a composite coating on a titanium-aluminum alloy surface in this example includes the following steps:

[0081] S1. Cut the Ti-45Al-8.5Nb ingot into Φ6×80mm round rods. Polish each side of the sample with SiC sandpaper and ultrasonically clean it with anhydrous ethanol for 5 minutes. After cleaning, dry the sample for later use.

[0082] S2. A WWL-PS DC regulated switching power supply is used. The electrolytic cell is a quartz glass container. The anode is connected to parallel sheet graphite plates. The sample to be processed, Ti-45Al-8.5Nb alloy substrate, is used as the cathode and placed at the center of the graphite electrode.

[0083] S3. Prepare an anhydrous ethanol solution of Al(NO3)3 and Ni(NO3)3, wherein the molar concentration ratio of the two is 5:1, and the Al(NO3)3 concentration is 1 mol / L. Pour the electrolyte into a quartz electrolytic cell. The cleaned sample is clamped on the cathode connection device, and the graphite sheet is clamped on the anode connection device. Turn on the power supply, set it to AC power mode, and set the deposition process parameters as follows: 200V deposition voltage, 80% deposition duty cycle, and 600s deposition time. After the deposition time is up, turn off the power supply, remove the sample, and ultrasonically clean it with anhydrous ethanol, then dry it with a hairdryer.

[0084] like Figure 7 As shown, the surface and cross-sectional morphology of the deposited Al2O3+Ni composite coating are presented, where, as Figure 7 As shown in (a), the number of pores on the coating surface is significantly reduced, and the pore size is also smaller. This is partly due to the addition of Ni, which makes the Ni particles themselves conductive, allowing them to act as discharge channels through metallic Ni. On the other hand, the addition of Ni can fill the pore locations within the coating itself, reducing the number of pores and sealing the pore structure of the coating; that is, in this embodiment, Ni fills the pore structure of Al2O3. Figure 7 The upper right inset of (a) is a magnified view of part A in the figure. It can be seen that there are no obvious cracks on the coating surface, and many small particles are clustered around the large particles.

[0085] like Figure 7 As shown in (b), the composite coating is well bonded to the titanium-aluminum alloy substrate and there are no obvious cracks. The average thickness of the composite coating is 19.38 μm. Although its thickness is reduced, its high-temperature oxidation resistance is greatly improved because the composite coating does not have a porous structure.

[0086] like Figure 8 The high-temperature oxidation resistance of the deposited Al2O3-Ni composite coating is shown in the figure. It can be seen that after 100 h of high-temperature oxidation, the Al2O3-Ni composite coating only increases in weight by 0.52 mg / cm³. 2 It is much smaller than the 0.94 mg / cm³ of the alloy matrix. 2 Therefore, this composite coating can significantly improve the high-temperature oxidation resistance of the material.

[0087] Combined Figure 5 , 6As shown in Figures 9, the surface morphology characterization results of the composite coating after 100 hours of high-temperature oxidation are presented. It can be seen that no obvious cracking phenomenon occurred on the surface of the coating after thermal oxidation. Compared with the untreated titanium-aluminum alloy and the titanium-aluminum alloy with Al2O3 coating, the sample surface of this embodiment does not have a large number of TiO2 particles generated, and has better high-temperature oxidation resistance.

[0088] This invention proposes a method for depositing coatings on the surface of titanium-aluminum alloys, which has the following beneficial effects:

[0089] This invention employs cathodic plasma electrolytic deposition technology to form a composite coating on the surface of titanium-aluminum alloy. Electrolytic breakdown occurs in relatively weak areas of the coating, thereby forming a continuous and dense composite coating on the surface of the titanium-aluminum alloy substrate. This significantly improves the high-temperature oxidation resistance of the material, with an application temperature exceeding 900℃. Furthermore, the preparation process of this invention is simple, time-saving, and can effectively control the composition and content of the composite coating.

[0090] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for depositing a composite coating on the surface of a titanium-aluminum alloy, characterized in that, The method includes: The titanium-aluminum alloy was subjected to at least two melting processes as samples to be processed; A graphite plate is used as the anode, and the sample to be treated is used as the cathode. The sample to be treated is connected to the graphite plate via an electrolyte. The electrolyte is an Al(NO3)3 and Y(NO3)3 solution. An Al2O3-Y2O3 composite coating is deposited on the surface of the titanium-aluminum alloy by a cathode plasma electrolytic deposition process. The composite coating has a porous structure. Alternatively, the electrolyte may be an Al(NO3)3 and Ni(NO3)2 solution; A composite coating is deposited on the surface of the titanium-aluminum alloy using a cathode plasma electrolytic deposition process; the application temperature of the composite coating is higher than 900°C. When the electrolyte is an aqueous solution, the deposition voltage of the cathode plasma electrolytic deposition process is 180V–220V, the deposition time is 500s–700s, and the duty cycle is 70%–90%; or, When the electrolyte is a low-surface-tension organic solvent, the deposition voltage of the cathode plasma electrolytic deposition process is 110V to 150V, the deposition time is 50s to 70s, and the duty cycle is 50% to 70%.

2. The method according to claim 1, characterized in that, The thickness of the Al2O3-Y2O3 composite coating ranges from 23.01 μm to 24.04 μm.

3. The method according to claim 1, characterized in that, The molar concentration ratio of Y(NO3)3 to Al(NO3)3 in the Al(NO3)3 and Y(NO3)3 solutions is 1:(19-21).

4. The method according to claim 1, characterized in that, When the electrolyte is an anhydrous ethanol solution of Al(NO3)3 and Ni(NO3)2, an Al2O3-Ni composite coating is deposited on the surface of the titanium-aluminum alloy by a cathode plasma electrolytic deposition process, and Ni is deposited in the porous structure of the composite coating.

5. The method according to claim 4, characterized in that, The thickness of the Al2O3-Ni composite coating ranges from 18 μm to 21 μm.

6. The method according to claim 4, characterized in that, The molar concentration ratio of Al(NO3)3 to Ni(NO3)2 in the Al(NO3)3 and Ni(NO3)2 solutions is (4-6):

1.

7. The method according to any one of claims 1 to 6, characterized in that, The titanium-aluminum alloy is Ti-45Al-8.5Nb.

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