Titanium alloy surface anti-oxidation coating and preparation method

Abstract

The invention belongs to the technical field of protective coatings, and particularly relates to a titanium alloy surface anti-oxidation coating and a preparation method. The diffusion aluminide coating with the aluminum content gradually reduced from outside to inside is prepared on the surface of the titanium alloy, and the coating is free of penetrating cracks and can contain elements such as Si. Firstly, an aluminum or aluminum alloy coating is pre-deposited on the surface of the titanium alloy, and then the diffusion aluminide coating is prepared through thermal diffusion treatment under vacuum. By adopting the method, not only is the prepared coating free of penetrating cracks, but also the formation of the cracks is inhibited in the thermal cycle process, and the high-temperature oxidation resistance of the coating is excellent.

Description

Technical Field

[0001] The invention belongs to the technical field of protective coatings, and specifically relates to an anti-oxidation coating on the surface of a titanium alloy and a preparation method thereof. Background Art

[0002] Titanium alloy has low density and high strength, and is a key material for aircraft engine compressors and other components. In terms of the high-temperature creep or strength properties of titanium alloys developed so far, their service temperature can reach up to about 600°C, but restricted by their anti-oxidation properties, the current service temperature limit of titanium alloy is about 500°C. When serving for a long time at high temperatures, a thick brittle dissolved oxygen layer will form on the surface of the titanium alloy, resulting in a significant decrease in the mechanical properties of the alloy. In order to improve the oxidation resistance of titanium alloys, applying a suitable protective coating is one of the effective ways. As a high-temperature anti-oxidation coating, diffusion aluminide coating has been widely used in high-temperature corrosion protection of high-temperature alloy components. However, when the diffusion aluminide coating is applied to the high-temperature oxidation protection of titanium alloys, since the diffusion aluminide coating formed on the surface of the titanium alloy is composed of TiAl with greater brittleness, 3 Phase composition, it is very easy to form through cracks during the formation process. Moreover, in the subsequent thermal cycle process, the difference in thermal expansion coefficients between the coating and the titanium alloy substrate leads to a significant increase in the number of through cracks in the coating (Reference ① Md. Zafir Alam, Dipak K. Das, Effect of cracking indiffusion aluminide coatings on their cyclic oxidation performance on Ti-based IMI-834 alloy, Corrosion Science 51 (2009) 1405-1412), and the oxidation resistance of the coating is significantly reduced. Summary of the invention:

[0003] The purpose of the present invention is to provide an anti-oxidation coating on the surface of a titanium alloy and a preparation method thereof, and to prepare a diffusion aluminide coating on the surface of the titanium alloy in which the Al content gradually decreases from the surface to the inside. The diffusion aluminide coating can inhibit the formation of through cracks during thermal cycling and significantly improve the high-temperature oxidation resistance of the titanium alloy.

[0004] The technical solution of the present invention is:

[0005] The invention discloses an anti-oxidation coating on the surface of a titanium alloy. A diffusion aluminide coating with aluminum content gradually decreasing from the surface to the inside is prepared on the surface of the titanium alloy, and there are no through cracks in the coating.

[0006] The titanium alloy surface anti-oxidation coating has a coating thickness of 10 to 40 μm.

[0007] The titanium alloy surface anti-oxidation coating contains Si element.

[0008] The method for preparing the anti-oxidation coating on the surface of titanium alloy comprises the following steps: firstly, pre-depositing aluminum or its alloy coating on the surface of titanium alloy, and then performing thermal diffusion treatment under vacuum to prepare a diffused aluminide coating.

[0009] The method for preparing the anti-oxidation coating on the surface of the titanium alloy, the method for pre-depositing aluminum or its alloy coating on the surface of the titanium alloy includes but is not limited to ion plating, sputtering, cold spraying or thermal spraying.

[0010] In the method for preparing the anti-oxidation coating on the surface of titanium alloy, the temperature range of the heat diffusion treatment under vacuum is 850° C. to 950° C., the annealing time is 30 minutes to 3 hours, and the coating is cooled along with the furnace.

[0011] The method for preparing the anti-oxidation coating on the surface of the titanium alloy comprises performing thermal diffusion treatment in a vacuum annealing furnace, wherein the pressure in the vacuum annealing furnace is 7×10 -3 Below Pa.

[0012] The design concept of the present invention is:

[0013] The present invention pre-deposits aluminum or its alloy coating on the surface of the titanium alloy and performs vacuum thermal diffusion treatment within a specified heat treatment temperature and time range to obtain a diffusion aluminide coating (e.g., 80 at.% to 20 at.%) with Al content gradually decreasing from the surface to the inside. The diffusion aluminide coating has a high degree of matching thermal expansion coefficient with the titanium alloy substrate and is less brittle. Not only does the prepared coating have no through cracks, but the formation of cracks is also suppressed during the thermal cycle process, and the coating has excellent high-temperature oxidation resistance.

[0014] The advantages and beneficial effects of the present invention are:

[0015] 1. In order to improve the high-temperature oxidation resistance of titanium alloy, the present invention designs and prepares a diffusion aluminide coating with Al content gradually decreasing from the surface to the inside. Not only does the prepared coating have no through cracks, but the formation of cracks is also suppressed during the thermal cycle process, and the coating has excellent high-temperature oxidation resistance.

[0016] 2. The anti-oxidation coating on the titanium alloy surface of the present invention has excellent anti-oxidation performance, a simple and easy-to-implement preparation process, no harmful substances are used or released during the preparation process, and is green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 (a) is a macroscopic photograph and (b) SEM cross-sectional morphology of the diffusion aluminide coating prepared on the titanium alloy in Example 1.

[0018] Figure 2(a) is a macroscopic photograph and (b) SEM cross-sectional morphology of the diffusion aluminide coating prepared on the titanium alloy in Example 2.

[0019] Figure 3 (a) is a macroscopic photograph and (b) SEM cross-sectional morphology of the diffusion aluminide coating prepared on the titanium alloy in Example 3.

[0020] Figure 4 The SEM surface (a) and cross-sectional morphology (b) of the diffusion aluminide coating prepared on the titanium alloy in Example 3 after cyclic oxidation at 750°C for 100 hours. DETAILED DESCRIPTION

[0021] In order to further understand the present invention, the present invention is described below in conjunction with examples, but the examples are only for further elaboration of the features and advantages of the present invention, rather than for limiting the claims of the present invention.

[0022] Example 1

[0023] In this embodiment, Ti-6Al-4V alloy is used as the substrate to prepare the anti-oxidation coating, and the specific steps are as follows:

[0024] (1) Preparation of pure aluminum target: A pure aluminum target prepared by vacuum melting method is used as cathode target, and the purity of the target is 99.9 wt%.

[0025] (2) Workpiece pretreatment: The base alloy was cut into samples of 15 mm × 10 mm × 2 mm, ground, and ultrasonically cleaned in a mixed solution of alcohol and acetone in a volume ratio of 1:1. The samples were blown dry and set aside for later use.

[0026] (3) Aluminum coating: Al coating is deposited using multi-arc ion plating equipment. The coating steps are as follows:

[0027] ①The titanium alloy sample is hung on the sample rack facing the aluminum target, and the vacuum device is turned on. When the vacuum chamber pressure is ≤1×10 -1 Pa, and start heating until the vacuum chamber temperature stabilizes at 200°C and the pressure is ≤7.0×10 -3 After 0.04 Pa, the sample holder was turned on and argon gas was introduced to maintain the pressure of the vacuum chamber at about 4.0 Pa. The bias power supply was turned on and the specimen was bombarded at a bias of -800 V for 3 minutes, and then the bias power supply was turned off.

[0028] ② Keep the sample holder rotating, adjust the gas flowmeter to maintain the vacuum chamber pressure at about 1.0Pa, turn on the bias power supply, turn on the aluminum target arc power supply, and deposit the aluminum coating. The specific process parameters are: arc current 90A, voltage 19V, substrate bias -50V, duty cycle 20%, deposition time 60min, turn off the arc power supply and bias power supply, and close the argon valve.

[0029] ③Maintain vacuum chamber pressure ≤7.0×10 -3 Pa, wait for the vacuum chamber temperature to cool down to below 100 °C, turn off the sample holder rotation, take out the titanium alloy specimen, and complete the aluminum coating preparation.

[0030] (4) Vacuum thermal diffusion treatment

[0031] The aluminum coating sample was placed in a vacuum annealing furnace and the pressure in the furnace reached 7.0×10 -3 Pa, raise the annealing furnace temperature to 900℃, keep it warm for 1 hour, and then turn off the annealing furnace heating device. Keep the pressure in the annealing furnace ≤7.0×10 -3 Pa, after the sample has cooled to room temperature, take out the sample.

[0032] (5) Coating structure characterization

[0033] The macroscopic photograph of the coating sample after thermal diffusion treatment is shown in Figure 1 (a), scanning electron microscopy (SEM) cross-sectional morphology Figure 1 (b), the energy spectrum analysis results of the marked points in the cross section are shown in Table 1.

[0034] Table 1 Figure 1 Energy spectrum analysis results of the indicated points (at.%)

[0035] Al Ti V 1 73.75 24.72 1.53 2 65.22 33.61 1.17 3 48.81 48.41 2.78 4 23.25 74.07 2.68

[0036] Depend on Figure 1 As can be seen from Table 1, the total thickness of the diffusion aluminide coating is about 13 microns, the aluminum content in the coating gradually decreases from the surface to the inside (73.75at.%), the titanium content in the coating gradually increases from the surface to the inside (24.72at.%), and no through cracks are observed in the coating.

[0037] Example 2

[0038] In this embodiment, Ti-6Al-4V alloy is used as the substrate to prepare the anti-oxidation coating, and the specific steps are as follows:

[0039] (1) Preparation of Al-Si alloy target: An Al-Si alloy target prepared by vacuum melting is used as a cathode target. The composition of the Al-Si alloy target is Al-5.2wt.%Si, and the purity of the target is 99.9wt%.

[0040] (2) Workpiece pretreatment: The base alloy was cut into samples of 15 mm × 10 mm × 2 mm, ground, and ultrasonically cleaned in a mixed solution of alcohol and acetone in a volume ratio of 1:1. The samples were blown dry and set aside for later use.

[0041] (3) Aluminum-silicon coating: Al-5.2wt.%Si coating is deposited by multi-arc ion plating equipment. The coating steps are as follows:

[0042] ①The titanium alloy sample is hung on the sample rack facing the aluminum silicon target, and the vacuum device is turned on. When the vacuum chamber pressure is ≤1×10 -1 Pa, and start heating until the vacuum chamber temperature stabilizes at 200°C and the pressure is ≤7.0×10 -3 After 0.04 Pa, the sample holder was turned on and argon gas was introduced to maintain the pressure of the vacuum chamber at about 4.0 Pa. The bias power supply was turned on and the specimen was bombarded at a bias of -800 V for 3 minutes, and then the bias power supply was turned off.

[0043] ② Keep the sample holder rotating, adjust the gas flowmeter to maintain the vacuum chamber pressure at about 1.0Pa, turn on the bias power supply, turn on the aluminum silicon target arc power supply, and deposit the aluminum silicon coating. The specific process parameters are: arc current 85A, voltage 19V, substrate bias -50V, duty cycle 20%, deposition time 50min, turn off the arc power supply and bias power supply, and close the argon valve.

[0044] ③Maintain vacuum chamber pressure ≤7.0×10 -3 Pa, wait for the vacuum chamber temperature to cool down to below 100 °C, turn off the sample holder rotation, take out the titanium alloy specimen, and complete the preparation of the aluminum-silicon coating.

[0045] (4) Vacuum thermal diffusion treatment

[0046] The aluminum-silicon coating sample was placed in a vacuum annealing furnace and the pressure in the furnace reached 7.0×10 -3 Pa, raise the annealing furnace temperature to 900℃, keep it warm for 1 hour, and then turn off the annealing furnace heating device. Keep the pressure in the annealing furnace ≤7.0×10 - 3 Pa, after the sample has cooled to room temperature, take out the sample.

[0047] (5) Coating structure characterization

[0048] The macroscopic photograph of the coating sample after thermal diffusion treatment is shown in Figure 2 (a), scanning electron microscopy (SEM) cross-sectional morphology Figure 2 (b), the energy spectrum analysis results of the marked points in the cross section are shown in Table 2.

[0049] Table 2 Figure 2 Energy spectrum analysis results of the indicated points (at.%)

[0050]

[0051]

[0052] Depend on Figure 2As can be seen from Table 2, the total thickness of the diffusion aluminide coating is about 13 microns, the aluminum content in the coating gradually decreases from the surface to the inside (66.55at.%), the silicon content in the coating gradually decreases from the surface to the inside (4.08at.%), the titanium content in the coating gradually increases from the surface to the inside (28.07at.%), and no through cracks are observed in the coating.

[0053] Example 3

[0054] In this embodiment, Ti-6Al-4V alloy is used as the substrate to prepare the anti-oxidation coating, and the specific steps are as follows:

[0055] (1) Preparation of Al-Si alloy target: An Al-Si alloy target prepared by vacuum melting is used as a cathode target. The composition of the Al-Si alloy target is Al-12.5wt.% Si, and the purity of the target is 99.9wt%.

[0056] (2) Workpiece pretreatment: The base alloy was cut into samples of 15 mm × 10 mm × 2 mm, ground, and ultrasonically cleaned in a mixed solution of alcohol and acetone in a volume ratio of 1:1. The samples were blown dry and set aside for later use.

[0057] (3) Aluminum-silicon coating: Al-12.5wt.% Si coating is deposited using multi-arc ion plating equipment. The coating steps are as follows:

[0058] ①The titanium alloy sample is hung on the sample rack facing the aluminum silicon target, and the vacuum device is turned on. When the vacuum chamber pressure is ≤1×10 -1 Pa, and start heating until the vacuum chamber temperature stabilizes at 200°C and the pressure is ≤7.0×10 -3 After 0.04 Pa, the sample holder was turned on and argon gas was introduced to maintain the pressure of the vacuum chamber at about 4.0 Pa. The bias power supply was turned on and the specimen was bombarded at a bias of -800 V for 3 minutes, and then the bias power supply was turned off.

[0059] ② Keep the sample holder rotating, adjust the gas flowmeter to maintain the vacuum chamber pressure at about 1.0Pa, turn on the bias power supply, turn on the aluminum silicon target arc power supply, and deposit the aluminum silicon coating. The specific process parameters are: arc current 85A, voltage 19V, substrate bias -200V, duty cycle 20%, deposition time 47min, turn off the arc power supply and bias power supply, and close the argon valve.

[0060] ③Maintain vacuum chamber pressure ≤7.0×10 -3 Pa, wait for the vacuum chamber temperature to cool down to below 100 °C, turn off the sample holder rotation, take out the titanium alloy specimen, and complete the preparation of the aluminum-silicon coating.

[0061] (4) Vacuum thermal diffusion treatment

[0062] The aluminum-silicon coating sample was placed in a vacuum annealing furnace and the pressure in the furnace reached 7.0×10 -3 Pa, raise the annealing furnace temperature to 900℃, keep it warm for 1 hour, and then turn off the annealing furnace heating device. Keep the pressure in the annealing furnace ≤7.0×10 - 3 Pa, after the sample has cooled to room temperature, take out the sample.

[0063] (5) Coating structure characterization and performance testing

[0064] The macroscopic photograph of the coating sample after thermal diffusion treatment is shown in Figure 3 (a), scanning electron microscopy (SEM) cross-sectional morphology Figure 3 (b), the energy spectrum analysis results of the marked points in the cross section are shown in Table 3.

[0065] Table 3 Figure 3 Energy spectrum analysis results of the indicated points (at.%)

[0066] Al Si Ti V 1 67.8 4.81 26.55 0.84 2 49.55 11.31 36.91 2.23 3 43.47 4.97 48.97 2.59 4 20.96 0.95 75.85 2.24

[0067] Depend on Figure 3 As shown in Table 3, the total thickness of the diffusion aluminide coating is about 13 microns, the aluminum content in the coating gradually decreases from the surface to the inside (67.8at.%~20.96at.%), and the titanium content in the coating gradually increases from the surface to the inside (26.55at.%~75.85at.%). No through cracks are observed in the coating. After cyclic oxidation at 750℃ for 100 hours, the surface and cross-sectional morphologies of the coating samples are shown in Table 3. Figure 4 The energy spectrum analysis results of the marked points in the cross section are shown in Table 4.

[0068] Table 4 Figure 4 Energy spectrum analysis results of the indicated points (at.%)

[0069] O Al Si Ti V 1 61.66 21.67 3.8 12.07 0.8 2 56.67 10.46 5.04 26.25 1.58 3 21.42 26.39 5.1 43.84 3.25 4 38.25 5.32 53.24 3.19 5 38.16 6.27 52.26 3.31 6 22.18 0.6 74.34 2.88

[0070] Depend on Figure 4 As shown in Table 4, after cyclic oxidation, the coating and the surface oxide film did not crack or peel off. The surface oxide film was composed of mixed oxides of aluminum oxide and titanium oxide, and the coating had excellent antioxidant properties.

[0071] The implementation results show that the anti-oxidation coating of the present invention is a diffusion aluminide coating, which may contain elements such as Si, and the aluminum content in the coating gradually decreases from the surface to the inside. First, aluminum or its alloy coating is pre-deposited on the surface of the titanium alloy, and then vacuum thermal diffusion treatment is performed. The prepared coating has no through cracks and has excellent high-temperature anti-oxidation performance.

Claims

1. An anti-oxidation coating on the surface of titanium alloy, It is characterized in that A diffusion aluminide coating with aluminum content gradually decreasing from the surface to the inside is prepared on the surface of the titanium alloy, and there are no through cracks in the coating.

2. The titanium alloy surface anti-oxidation coating according to claim 1, It is characterized in that The coating thickness is 10 to 40 μm.

3. The anti-oxidation coating on the titanium alloy surface according to claim 1, It is characterized in that The coating contains Si element.

4. A method for preparing the anti-oxidation coating on the surface of titanium alloy according to claim 1, It is characterized in that Firstly, aluminum or its alloy coating is pre-deposited on the surface of titanium alloy, and then a diffusion aluminide coating is prepared by thermal diffusion treatment under vacuum.

5. The method for preparing the anti-oxidation coating on the surface of titanium alloy according to claim 4, It is characterized in that Methods for pre-depositing aluminum or its alloy coating on the titanium alloy surface include, but are not limited to, ion plating, sputtering, cold spraying or thermal spraying.

6. The method for preparing the anti-oxidation coating on the surface of titanium alloy according to claim 4, It is characterized in that The temperature range of the thermal diffusion treatment under vacuum is 850° C. to 950° C., the annealing time is 30 minutes to 3 hours, and the furnace is cooled.

7. The method for preparing the anti-oxidation coating on the surface of titanium alloy according to claim 6, It is characterized in that Thermal diffusion treatment is carried out in a vacuum annealing furnace with an air pressure of 7×10 -3 Below Pa.

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