Titanium alloy surface high-temperature protective coating and integrated preparation method

Abstract

The application discloses a titanium alloy surface high-temperature protective coating and an integrated preparation method, and belongs to the technical field of material high-temperature protective coating. x The coating is combined on the surface of a titanium alloy base body, and sequentially comprises a diffusion aluminide TiAl x bottom layer and an Al2O3 surface layer from inside to outside; the thickness of the bottom layer is 3-20 micrometers, and the thickness of the surface layer is 1-10 micrometers. The preparation method is integrally completed by using a multi-arc ion plating technology, and comprises the following steps: performing plasma cleaning and activation on the surface of the base body; preparing the diffusion aluminide TiAl x bottom layer on the activated surface by alternately performing a low-bias deposition step and a high-bias bombardment step; then introducing oxygen, and preparing the Al2O3 surface layer by reaction deposition. The method is coherent in process and friendly to the environment, the prepared composite coating is firm in combination, compact in structure, and can effectively improve the service life of the titanium alloy in a high-temperature oxidation environment.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature protective coating technology, specifically relating to a high-temperature protective coating for titanium alloy surfaces and an integrated preparation method thereon. Background Technology

[0002] Titanium alloys, with their high specific strength and good corrosion resistance, are widely used in aerospace and other fields to manufacture critical structural components such as engine hot-section parts. However, when titanium alloys are used for extended periods in oxygen-rich environments exceeding 600 degrees Celsius, the protective effect of the TiO2 oxide film formed on their surface deteriorates (Das DK, et al. Surface & Coatings Technology, 2006, 201: 3406-3414). Simultaneously, oxygen atoms, with their high solid solubility in titanium alloys, continuously diffuse into the matrix, leading to the formation of a brittle oxygen-rich layer on the surface, resulting in a decrease in the alloy's plasticity, fatigue strength, and other mechanical properties. This phenomenon severely restricts the reliable application of titanium alloys in higher temperature environments.

[0003] Existing technologies often employ processes such as powder embedding aluminizing (Chaia N, et al. Journal of Phase Equilibria and Diffusion, 2020, 41(3):181-190), slurry aluminizing (Mcmordie B G. Surface & Coatings Technology, 1991, 49(1-3):18-23), or hot-dip galvanizing combined with heat treatment (Oukati Sadeq F, et al. Surface & Coatings Technology, 2018, 337:349-356). These methods aim to form a diffusion layer dominated by the TiAl3 phase on the surface of titanium alloys, utilizing it to generate an Al2O3 film at high temperatures to provide antioxidant protection. However, single aluminide coatings prepared using this traditional process have significant drawbacks: due to the difference in thermal expansion coefficients between the coating and the substrate, and the high brittleness of the TiAl3 layer, the coating is prone to developing penetrating microcracks during preparation or subsequent thermal cycling (Alam M Z, et al. Corrosion Science, 2009, 51(6): 1405-1412). The presence of cracks provides a channel for rapid internal diffusion of oxygen, thereby accelerating substrate oxidation and limiting the long-term protective effect of the coating.

[0004] To address the shortcomings of single aluminide coatings, some studies have attempted to modify them by introducing elements such as silicon and chromium (Cammarota G P, et al. Surface & Coatings Technology, 2006, 201(1-2):230-242), or to prepare composite coatings such as aluminum and silicon (Chen C, et al. Journal of Alloys & Compounds, 2017, 701:27-36). However, these improvement methods often involve complex processes or require multiple independent processing steps, which affects production efficiency.

[0005] Therefore, how to obtain a high-temperature protective coating on the surface of titanium alloys with high bonding strength, dense and complete structure, and long-term effective oxygen diffusion barrier, while making the preparation process more efficient, integrated and environmentally friendly, is a technical problem that needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a high-temperature protective coating for titanium alloy surfaces and an integrated preparation method thereon.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A high-temperature protective coating for titanium alloy surfaces, wherein the coating is laminated onto the surface of a titanium alloy substrate, and consists of diffused aluminide TiAl from the inside out. x The bottom layer and the Al2O3 top layer; the diffused aluminide TiAl x The thickness of the bottom layer is 3-20 μm, and the thickness of the Al2O3 surface layer is 1-10 μm.

[0008] Furthermore, the diffused aluminide TiAl x The underlying layer consists of one or more of the TiAl3, TiAl2, and TiAl phases.

[0009] Furthermore, the diffused aluminide TiAl x The bottom layer also contains at least one element from Si and Cr.

[0010] An integrated method for preparing a high-temperature protective coating on a titanium alloy surface employs multi-arc ion plating technology to sequentially prepare diffused aluminum compounds (TiAl) on the surface of a titanium alloy substrate. x The process includes the following steps: (Base layer and Al2O3 top layer) (1) Plasma cleaning and activation of the surface of the titanium alloy substrate; (2) Preparation of diffused aluminides TiAl on the surface of activated titanium alloy matrix x bottom layer; (3) In the diffused aluminide TiAl x An Al2O3 surface layer was prepared on the bottom surface.

[0011] Furthermore, in step (1), the plasma cleaning and activation specifically involves: the vacuum level inside the multi-arc ion plating chamber reaching 7.0 × 10⁻⁶. -3 After Pa, argon gas is introduced to maintain the gas pressure at 2.0-6.0 Pa, and a pulse bias voltage of -700V to -1000V is applied to bombard the titanium alloy matrix for 5-15 minutes.

[0012] Furthermore, in step (2), the diffused aluminide TiAl x The preparation of the underlying layer is carried out by alternating between low-bias deposition steps and high-bias bombardment steps.

[0013] Furthermore, the parameters for the low-bias deposition step are as follows: the gas pressure in the chamber is maintained at 2.0-6.0 Pa, an aluminum target is used as the cathode target, the arc current is 90-180 A, a pulse bias voltage of 0 V to -200 V is applied to the substrate, and the deposition time is 2-10 min.

[0014] Furthermore, the parameters for the high-bias bombardment step are as follows: the gas pressure in the chamber is maintained at 2.0-6.0 Pa, an aluminum target is used as the cathode target, the arc current is 90-180 A, a pulse bias voltage of -400 V to -900 V is applied to the substrate, and the bombardment time is 3-30 min.

[0015] Further, in step (3), the preparation of the Al2O3 surface layer is specifically as follows: oxygen and argon are simultaneously introduced into the chamber of the multi-arc ion plating equipment, the chamber pressure is maintained at 1.0-3.0 Pa, an aluminum target is used as the cathode target, the arc current is 70-80 A, a pulse bias voltage of 0 V to -200 V is applied to the substrate, and the deposition time is 15-150 min.

[0016] Furthermore, the diffused aluminide TiAl x The thickness of the bottom layer is 3-20 μm, and the thickness of the Al2O3 surface layer is 1-10 μm.

[0017] Beneficial effects of this invention: 1. The composite coating structure designed in this invention utilizes diffused aluminide TiAl x The combination of the underlying layer and the outer Al2O3 surface layer provides multi-layered protection. The diffusion-based underlayer forms a metallurgical bond with the titanium alloy substrate, resulting in a strong interfacial bond and a certain degree of self-oxidation resistance. The outer Al2O3 surface layer has a dense structure and good thermal stability, directly preventing the intrusion of oxygen from the environment. This structure makes the coating system more durable and reliable. Even if the surface layer is damaged locally, the underlying aluminide underlayer can still provide some protection, thereby extending the effective service life of the coating in high-temperature oxidizing environments.

[0018] 2. This invention employs multi-arc ion plating technology, achieving integrated fabrication by continuously performing plasma cleaning and activation, diffusion underlayer preparation, and Al2O3 surface layer deposition within a single device. This tightly integrated process avoids surface contamination or oxidation caused by workpiece transfer between different processes, thus ensuring the cleanliness and bonding quality of the interlayer interfaces. The entire process is completed in a vacuum environment, eliminating the need for harmful chemicals such as halides used in traditional aluminizing processes, meeting clean production requirements. Process parameters are easily and precisely controlled, facilitating the repeatable preparation of coating thickness and structure.

[0019] 3. In the preparation of the diffused aluminide underlayer, the present invention uses alternating low bias deposition and high bias bombardment processes to promote the diffusion of aluminum atoms to the substrate surface by utilizing the bombardment effect of high-energy ions, which helps to form a uniform and dense diffusion layer.

[0020] 4. The preparation method of this invention has good flexibility in composition control. During the preparation process, by selecting an alloy target containing specific elements such as silicon and chromium, beneficial alloying elements can be incorporated into the diffused aluminide substrate. This allows the coating properties, such as oxidation resistance, hot corrosion resistance, or thermal expansion matching with the substrate, to be specifically designed and optimized according to the specific titanium alloy material and service environment conditions. Attached Figure Description

[0021] Figure 1 The image shows the cross-sectional morphology of the composite coating prepared on the titanium alloy surface in Example 1 and its cross-sectional morphology after 1000 cycles of oxidation at 750°C.

[0022] Figure 2 The image shows the cross-sectional morphology of the diffused aluminide coating prepared on the titanium alloy surface in Comparative Example 1 and its cross-sectional morphology after 1000 cycles of oxidation at 750℃. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be noted that the embodiments described below are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] This invention provides a high-temperature protective coating for titanium alloy surfaces and its integrated preparation method. The coating is composed of diffused aluminum oxide TiAl. x It consists of an inner and outer Al2O3 surface layer, and is continuously prepared within the same vacuum cycle using multi-arc ion plating technology.

[0025] Example 1 I. Coating Preparation Using Ti65 titanium alloy sheet as the substrate, a coating was prepared using a multi-arc ion plating device. The specific steps are as follows: 1. Pre-treatment of workpieces: Cut Ti65 alloy into samples with dimensions of 15mm×10mm×2mm. Grind the surface with sandpaper step by step until it is smooth, then place it in a mixed solution of alcohol and acetone for ultrasonic cleaning. After cleaning, dry it with hot air for later use.

[0026] 2. Equipment and Target Preparation: A multi-arc ion plating system equipped with a pure aluminum target (99.9% purity) is used. The cleaned sample is fixed on the sample holder inside the vacuum chamber, ensuring the sample is directly aligned with the aluminum target. The chamber is then closed, and vacuuming begins.

[0027] 3. Plasma cleaning and activation: When the vacuum degree reaches 7.0 × 10⁻⁶ -3 After Pa, argon gas is introduced into the chamber to stabilize the working pressure at 4.0 Pa. The sample holder is then rotated, and a pulsed bias voltage is applied to the sample for bombardment. First, bombardment is performed for 5 minutes at a bias voltage of -800V and a duty cycle of 40%. Subsequently, while maintaining the gas pressure, the aluminum target arc source is turned on, the arc current is set to 150A, and the sample bias voltage is adjusted to -900V and a duty cycle of 20%, continuing bombardment for another 3 minutes. This step is used to clean and activate the surface of the titanium alloy substrate.

[0028] 4. Preparation of diffused aluminides TiAl x Substrate: After activation, the chamber pressure was maintained at 4.0 Pa, and the aluminum target arc current was kept at 150 A. The substrate was prepared by alternating low-bias deposition and high-bias bombardment. Low bias deposition: The sample bias is rapidly adjusted to -50V, the duty cycle is 20%, and the deposition time is 3 minutes. During this stage, aluminum ions are deposited on the sample surface at a lower energy.

[0029] High bias voltage bombardment: The sample bias voltage is adjusted to -600V, the duty cycle is 50%, and the bombardment time is 15 minutes. During this stage, high-energy ions bombard the newly deposited aluminum layer, promoting the diffusion of aluminum into the titanium alloy matrix.

[0030] This deposition-bombardment cycle is performed once. After completion, the arc source and bias power supply are turned off, and the argon gas supply is stopped. At this point, the temperature inside the chamber is approximately 320°C.

[0031] 5. Preparation of Al2O3 surface layer: Wait for the chamber temperature to cool naturally to 200℃ and the vacuum degree to recover to ≤7.0×10⁻⁶. - 3Pa. Then, oxygen and argon were simultaneously introduced into the chamber at flow rates of 160 sccm and 20 sccm, respectively, to control the chamber pressure at 1.5 Pa. The aluminum target arc source was turned on, the arc current was set to 80 A, and a pulse bias voltage of -200 V and 20% duty cycle was applied to the sample for reaction deposition for 30 minutes. After deposition, all power and gas sources were turned off in sequence.

[0032] 6. Cooling and sampling: Maintain a high vacuum state and wait for the chamber temperature to cool down to below 100°C before stopping the sample holder rotation and taking out the prepared coating sample.

[0033] II. Coating Structure and Performance Characterization 1. Coating Structure Analysis: The cross-sectional morphology of the coating was observed using a scanning electron microscope (SEM). The results are as follows: Figure 1 As shown in (a), the total coating thickness is approximately 6.8 μm, exhibiting a clear two-layer structure. The inner layer, bonded to the substrate, is a diffusion layer with a thickness of approximately 4.6 μm, which, according to X-ray diffraction (XRD) analysis, is mainly composed of the TiAl3 phase. The outer layer is a dense Al2O3 layer with a thickness of approximately 2.2 μm. The two layers are tightly bonded, with a clear interface, and no obvious pores or cracks were observed.

[0034] 2. High-Temperature Oxidation Performance Test: The coated samples underwent a cyclic oxidation test in a static air environment at 750℃. Each cycle included holding the sample in the furnace for 1 hour, followed by cooling in air for 15 minutes. After 1000 cycles of oxidation, the cross-sectional morphology of the coating was observed again. Figure 1 As shown in (b), the Al2O3 surface layer is slightly thickened but remains continuous and intact. The internal TiAl3 diffusion layer has partially transformed into the TiAl phase, but the overall structure of the coating remains intact without peeling, and no obvious diffusion of oxygen into the titanium alloy matrix is ​​observed. This indicates that the composite coating provides effective long-term high-temperature protection for the substrate.

[0035] Comparative Example 1 I. Coating Preparation The substrate pretreatment, equipment preparation, plasma cleaning and activation steps are the same as in Example 1.

[0036] After the activation step, only the diffusion aluminide coating was prepared: under an argon atmosphere of 4.0 Pa, with the aluminum target arc current maintained at 150 A, a low-bias deposition was first performed at -50 V, 20% duty cycle, and 3 minutes, followed immediately by a high-bias bombardment at -600 V, 50% duty cycle, and 15 minutes. After completion, all power and gas sources were turned off, and samples were taken after cooling. No Al2O3 surface layer deposition was performed.

[0037] II. Coating Structure and Performance Characterization 1. Coating structure analysis: The cross-sectional morphology of the prepared single-diffusion aluminide coating is as follows: Figure 2 As shown in (a), the coating is a single TiAl3 diffusion layer with a thickness of approximately 4.6 μm. It is well bonded to the substrate, and no macroscopic cracks were observed in the initial state.

[0038] 2. High-temperature oxidation performance test: The test was conducted under the same conditions as in Example 1 (750℃, 1000 cycles of oxidation). The cross-sectional morphology of the oxidized coating is shown below. Figure 2 As shown in (b), significant degradation of the coating can be observed, with uneven oxide film thickness and accelerated oxidation in localized areas. Compared to... Figure 1 (b) In comparison, its high-temperature oxidation resistance is significantly inferior to that of the Al2O3 / TiAl3 composite coating in Example 1.

[0039] As can be seen from the above embodiments and comparative examples, the Al2O3 / TiAl provided by the present invention x The composite coating structure and its integrated preparation method can effectively improve the long-term oxidation resistance of titanium alloys at temperatures of 750℃ and above. This method features a consistent and highly controllable process, and the coating performance can be optimized by adjusting the target material composition and process parameters.

Claims

1. A high-temperature protective coating for titanium alloy surfaces, characterized in that, The coating is applied to the surface of a titanium alloy substrate, consisting of diffused aluminides TiAl from the inside out. x The bottom layer and the Al2O3 top layer; the diffused aluminide TiAl x The thickness of the bottom layer is 3-20 μm, and the thickness of the Al2O3 surface layer is 1-10 μm.

2. The high-temperature protective coating on the titanium alloy surface according to claim 1, characterized in that, The diffused aluminide TiAl x The underlying layer consists of one or more of the TiAl3, TiAl2, and TiAl phases.

3. The high-temperature protective coating on the titanium alloy surface according to claim 1 or 2, characterized in that, The diffused aluminide TiAl x The bottom layer also contains at least one element from Si and Cr.

4. An integrated preparation method for a high-temperature protective coating on a titanium alloy surface, characterized in that, Diffused aluminides (TiAl) were sequentially prepared on the surface of a titanium alloy substrate using multi-arc ion plating technology. x The process includes the following steps: (Base layer and Al2O3 top layer) (1) Plasma cleaning and activation of the surface of the titanium alloy substrate; (2) Preparation of diffused aluminides TiAl on the surface of activated titanium alloy matrix x bottom layer; (3) In the diffused aluminide TiAl x An Al2O3 surface layer was prepared on the bottom surface.

5. The integrated preparation method of the high-temperature protective coating on the titanium alloy surface according to claim 4, characterized in that, In step (1), the plasma cleaning and activation specifically involves: the vacuum level inside the multi-arc ion plating chamber reaching 7.0 × 10⁻⁶. -3 After Pa, argon gas is introduced to maintain the gas pressure at 2.0-6.0 Pa, and a pulse bias voltage of -700V to -1000V is applied to bombard the titanium alloy matrix for 5-15 minutes.

6. The integrated preparation method of the high-temperature protective coating on the surface of titanium alloy according to claim 4, characterized in that, In step (2), the diffused aluminide TiAl x The preparation of the underlying layer is carried out by alternating between low-bias deposition steps and high-bias bombardment steps.

7. The integrated preparation method of the high-temperature protective coating on the surface of titanium alloy according to claim 6, characterized in that, The parameters for the low-bias deposition step are as follows: the chamber pressure is maintained at 2.0-6.0 Pa, an aluminum target is used as the cathode target, the arc current is 90-180 A, a pulse bias voltage of 0 V to -200 V is applied to the substrate, and the deposition time is 2-10 min.

8. The integrated preparation method of the high-temperature protective coating on the surface of titanium alloy according to claim 6 or 7, characterized in that, The parameters for the high-bias bombardment step are as follows: the air pressure in the chamber is maintained at 2.0-6.0 Pa, an aluminum target is used as the cathode target, the arc current is 90-180 A, a pulse bias voltage of -400 V to -900 V is applied to the substrate, and the bombardment time is 3-30 min.

9. The integrated preparation method of the high-temperature protective coating on the surface of titanium alloy according to claim 4, characterized in that, In step (3), the preparation of the Al2O3 surface layer is specifically as follows: oxygen and argon are simultaneously introduced into the chamber of the multi-arc ion plating equipment, the chamber pressure is maintained at 1.0-3.0 Pa, an aluminum target is used as the cathode target, the arc current is 70-80 A, a pulse bias voltage of 0 V to -200 V is applied to the substrate, and the deposition time is 15-150 min.

10. The integrated preparation method of the high-temperature protective coating on the surface of titanium alloy according to claim 4, characterized in that, The diffused aluminide TiAl x The thickness of the bottom layer is 3-20 μm, and the thickness of the Al2O3 surface layer is 1-10 μm.

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