A method for preparing a Si-Hf-Yb co-deposition coating on a surface of a TiAl alloy

Abstract

The application discloses a method for preparing Si-Hf-Yb co-deposition coating on the surface of a TiAl alloy, and the co-deposition coating has a multilayer structure and is composed of an outer Hf and Yb rich silicide surface layer, a TiSi2+Ti5Si3 outer layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer and a TiAl2 inner layer from outside to inside. The method comprises the following steps: 1, preparing a pretreated TiAl alloy; 2, preparing a penetrant; 3, sealingly embedding the pretreated TiAl alloy into the penetrant; and 4, diffusion pack cementation. The method adopts the diffusion pack cementation process, controls the composition of the penetrant and the process conditions, realizes the simultaneous co-deposition of Hf and Yb and Si, makes Yb and Hf in the penetration layer doped into the SiO2 oxide film after oxidation, plays the role of optimizing the structure of the oxide film and inhibiting the growth of the oxide film, effectively improves the high-temperature oxidation resistance of the TiAl alloy, and is suitable for the field of aerospace.

Description

Technical Field

[0001] This invention belongs to the field of material surface coating and modification technology, specifically relating to a method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy. Background Technology

[0002] Compared with traditional titanium alloys and nickel-based superalloys, γ-TiAl-based intermetallic compound alloys have a lower density (3.9 g / cm³). 2 TiAl alloys, with their high elastic modulus, high specific strength, and good heat resistance and creep resistance, have become one of the most promising alloys for high-temperature components in aerospace engines. However, engines present harsh environments with high temperatures, high airflow, and strong gas corrosion, subjecting TiAl alloy components to intense high-temperature oxidation during service. The high Ti content in TiAl alloys prevents the formation of a continuous, dense Al2O3 protective film on their surface at high temperatures, instead producing a loose TiO2+Al2O3 oxide layer, which is insufficient to effectively protect the alloy components. As problems such as poor room-temperature plasticity hindering the application of TiAl alloys are gradually resolved, their oxidation resistance above 800℃ has become a key factor determining their serviceability.

[0003] Using coating technology for protection is the most effective and economical way to improve the high-temperature oxidation resistance of TiAl alloy. At present, the high-temperature oxidation resistance coating technology developed for TiAl alloy surface mainly focuses on diffusion aluminizing, plasma spraying, physical vapor deposition and other technologies (Qu Jing, Xie Faqin, Wu Xiangqing, et al. Research progress of high-temperature oxidation resistance coating of γ-TiAl alloy. Rare Metal Materials and Engineering, 2022, 51(10):3929-3936.). These technologies mainly have the following problems: (1) The thermal expansion coefficients of diffusion aluminizing coating and substrate are significantly different, which makes it easy to generate longitudinal through cracks; (2) Plasma spraying coating has poor adhesion to substrate and high porosity; (3) Physical vapor deposition methods such as ion plating and magnetron sputtering require specific equipment to prepare coatings. The equipment structure is complex and the equipment has great limitations on the shape and size of the substrate workpiece.

[0004] Silicide coatings exhibit low density, high melting point, and good thermal stability. At high temperatures, they can generate protective oxide SiO2, effectively improving the density and self-healing ability of the oxide film. Diffusion-embedding infiltration can produce silicide coatings with strong adhesion (metallurgical bonding), uniformity, and density. Furthermore, the embedding process is simple, requiring only a common high-temperature resistance furnace, resulting in low cost and minimal restrictions on the shape and size of the substrate, making it suitable for practical production and applications. However, TiAl alloy silicide coatings still have some limitations in application. For example, at high temperatures, the formation free energies of TiO2 and SiO2 are similar, resulting in the formation of loose, easily peeling TiO2; interdiffusion between the coating and the substrate alloying elements at high temperatures leads to coating degradation and reduces the coating's protective lifespan; and the mismatch in thermal expansion coefficients between the high-temperature generated oxide film and the coating makes it prone to cracking and peeling during thermal cycling oxidation.

[0005] Elemental doping modification of silicide coatings can optimize the coating microstructure and further improve its service performance. Studies have shown that Hf and Yb can effectively modify silicide coatings. W. Wang et al. prepared a Si-Al-Hf co-diffusion coating by embedding and infiltrating on the surface of Nb-Si based alloys. HfO2 particles generated by Hf oxidation are distributed at the interface between the oxide film and the coating, which can inhibit crack propagation caused by vacancy aggregation, thereby improving the adhesion of the oxide film (W. Wang, B. Zhang, C. Zhou. Formation and oxidation resistance of Hf and Al modified silicide coating on Nb-Si based alloy. Corrosion Science, 2014, 86: 304-309.). CC Wang et al. prepared a MoSi2-Yb2O3 composite coating on C / C composite materials by plasma spraying. 3+ It fills the voids in SiO2, increases the viscosity of SiO2, and inhibits the effective transport of oxygen in SiO2, thereby delaying the oxidation of the coating (C.-C.Wang,KZLi,D.-Y.He,et al.Oxidation behavior of plasma-sprayed MoSi2-Yb2O3 compositecoating at 1700℃.Ceramics International,2020,46(7):9538-9547.).

[0006] Currently, Hf and Yb modified silicide coatings are mainly used in ultra-high temperature structural materials such as Nb-Si based alloys and C / C composites, achieving good protective effects. However, the preparation of high-temperature oxidation-resistant Hf and Yb co-modified silicide coatings on TiAl alloy surfaces using a diffusion embedding process is still a gap in research. Although existing research suggests that the simultaneous addition of Hf and Yb has a good effect on improving the adhesion of the oxide film in silicide coatings and reducing the oxidation rate of the coating, the growth process of the coating is more complex than that of single silicide coatings because the adsorption and diffusion of the infiltrated elements (Si, Hf, Yb) on the substrate surface during the embedding process can affect each other. Therefore, further exploration and optimization of the preparation process are needed. Thus, developing a high-temperature oxidation-resistant Si-Hf-Yb co-infiltrating coating using a simple diffusion embedding technique is of great significance for the application of TiAl alloys in the aerospace industry. Summary of the Invention

[0007] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for preparing a Si-Hf-Yb co-diffusion coating on the surface of TiAl alloys. This method employs a diffusion-embedding infiltration process, combined with controlled infiltration agent composition and process conditions, to achieve simultaneous co-diffusion deposition of Hf, Yb, and Si. This allows the oxidized Yb and Hf in the infiltrated layer to be doped into the SiO2 oxide film, optimizing the oxide film microstructure and inhibiting oxide film growth. This effectively improves the high-temperature oxidation resistance of TiAl alloys, filling the gap in the development of high-temperature oxidation resistant Si-Hf-Yb co-diffusion coatings for TiAl alloy surfaces.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy, characterized in that the Si-Hf-Yb co-diffusion coating has a multi-layer structure, consisting of, from the outside to the inside, a silicide surface layer rich in Hf and Yb, a TiSi2+Ti5Si3 outer layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and a TiAl2 inner layer. The method includes the following steps:

[0009] Step 1: Grind the TiAl alloy step by step, then ultrasonically clean it in anhydrous ethanol or acetone, and dry it to obtain the pretreated TiAl alloy.

[0010] Step 2: Weigh the powders of Si, Hf, Yb2O3, NaF and Al2O3, mix, grind and dry them to prepare the infiltration agent;

[0011] Step 3: Put the carburizing agent prepared in Step 2 into the crucible, then embed the pretreated TiAl alloy from Step 1 into the carburizing agent in the crucible and compact it. Then cover the crucible and seal it with a high-temperature sealing mud made of silica sol and Al2O3 before placing it in a high-temperature resistance furnace.

[0012] Step 4: Heat and maintain the temperature of the crucible placed in the high-temperature resistance furnace in Step 3, so that the diffusion agent diffuses and embeds the TiAl alloy, and a Si-Hf-Yb co-diffusion coating is obtained on the surface of the TiAl alloy.

[0013] This invention involves embedding a TiAl alloy in a diffusion agent and sealing it under heat treatment. A Si-Hf-Yb co-diffusion coating is then prepared by diffusion embedding and co-diffusion onto the TiAl alloy surface. NaF in the diffusion agent acts as a diffusion catalyst, transporting active atoms to the TiAl alloy surface and promoting the growth of the diffusion layer. Specifically, during the heating and heat treatment process, NaF reacts with Hf, Yb₂O₃, and Si to generate Hf, Yb, and Si gaseous fluorides. These gaseous fluorides continuously diffuse into the TiAl alloy surface, releasing active atoms of Hf, Yb, and Si. These active atoms diffuse into the interior of the TiAl alloy substrate to form the co-diffusion coating, thus modifying the coating. Because Si has a smaller atomic radius and stronger diffusion ability than Hf and Yb, Si first reacts with Ti in the TiAl alloy to form a silicide surface layer, and then diffuses further inward to form a TiSi2+Ti5Si3 outer layer. Al in the TiAl alloy does not react with Si, but only accumulates below the outer layer as the outer layer grows, forming a TiAl2 inner layer. Diffusion between the TiSi2+Ti5Si3 outer layer and the TiAl2 inner layer forms a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer. Hf and Yb, with larger atomic radii, diffuse over shorter distances and only accumulate on the surface, forming a Hf- and Yb-rich silicide surface layer. Since Hf and Yb have larger atomic radii, adding appropriate amounts of Hf and Yb can form a substitutional solid solution in the coating, increasing the degree of lattice distortion, thereby further promoting the inward diffusion of Si and achieving modification of the silicide coating. In addition, Al2O3 in the penetrant of the present invention is a filler, which plays a role in dispersing NaF, Hf, Yb2O3 and Si powders and inhibiting the adhesion and caking of the penetrant.

[0014] The above-mentioned method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy is characterized in that, in step one, the TiAl alloy is polished step by step using 80# to 2000# SiC wet sandpaper, and the ultrasonic cleaning time is 0.25h to 0.5h.

[0015] The above-mentioned method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy is characterized in that, in step two, the powders are weighed according to the following mass percentages: Si 10%–20%, Hf 5%–15%, Yb₂O₃ 1%–5%, NaF 3%–10%, with the balance being Al₂O₃; the particle size of the Si, Hf, Yb₂O₃, and Al₂O₃ powders is less than 200 mesh, and the NaF is analytical grade. This invention is the first to simultaneously add Hf and Yb elements to a diffusion embedding agent to prepare a Si-Hf-Yb co-diffusion coating. By controlling the content of each component in the diffusion agent, especially the content of Hf and Yb₂O₃, sufficient Hf and Yb are ensured in the co-diffusion coating to achieve the modification effect on the coating. At the same time, excessive content is avoided, as it inhibits the penetration of Si, which is detrimental to the growth of the silicide coating and may even cause the co-diffusion coating to lose its high-temperature protective function.

[0016] The above-mentioned method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy is characterized in that the grinding time in step two is 2h to 4h, and the drying temperature is 100℃ and the drying time is 0.5h to 1h.

[0017] The above-mentioned method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy is characterized in that, in step three, the thickness of the infiltrator covering the surface of the pretreated TiAl alloy in the crucible after compaction and the distance between the pretreated TiAl alloy and the bottom of the crucible are both not less than 10 mm.

[0018] The above-mentioned method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy is characterized in that the mixing ratio of silica sol and Al2O3 in step three is: 1 kg to 1.5 kg of Al2O3 is added to every 1 L of silica sol with a mass concentration of 30% to 40%.

[0019] The above-mentioned method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy is characterized in that the heating and holding process in step four is as follows: heating from room temperature to 900℃ to 1100℃ at a heating rate of 5℃ / min to 10℃ / min and holding for 3h to 12h, and then taking the crucible out of the high-temperature resistance furnace and air-cooling it to room temperature. During the process of this invention, it was discovered that, given the significantly larger atomic radii of Hf and Yb compared to Si, diffusion in the co-diffusion coating is difficult. At temperatures below 900℃ or for durations less than 3 hours, Hf and Yb diffusion is difficult to achieve. At temperatures above 1100℃, severe interdiffusion occurs between the co-diffusion coating and the substrate, resulting in a porous coating that loses its protective function. Furthermore, excessively high temperatures significantly impact the microstructure and mechanical properties of the TiAl alloy substrate, rendering the co-diffusion coating preparation impractical. When the diffusion time exceeds 12 hours, a large amount of diffusion agent is consumed, and the co-diffusion coating ceases to grow. At times shorter than 3 hours, the deposition of Hf and Yb with large atomic radii is minimal, and the co-diffusion coating thickness is too small to provide protection. Therefore, this invention, by controlling the heating and holding temperature and time, ensures the co-diffusion of Hf, Yb, and Si on the TiAl alloy surface, forming a co-diffusion coating with excellent protective properties.

[0020] The above-mentioned method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy is characterized in that the TiAl alloy with the Si-Hf-Yb co-diffusion coating on the surface is taken out from the crucible after being cooled to room temperature, and ultrasonically cleaned in distilled water for 0.5h to 1h to remove residual infiltrator powder, and then placed in an oven at 100℃ for 0.5h to 1h to dry.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. This invention employs a diffusion-embedding infiltration process, combined with controlled infiltration agent composition and process conditions, to achieve simultaneous co-infiltration deposition of Hf, Yb, and Si. A co-infiltration coating is obtained on the TiAl alloy surface, consisting of a Hf- and Yb-rich silicide surface layer, a TiSi2+Ti5Si3 outer layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and a TiAl2 inner layer, arranged sequentially from the outside to the inside. During high-temperature oxidation, since Hf and Yb are mainly distributed on the surface layer, and the formation free energy of Hf and Yb oxides HfO2 and Yb2O3 is lower than that of Ti and Si oxides TiO2 and SiO2, Yb and Hf in the infiltration layer are preferentially oxidized at high temperatures to form Yb2O3 and HfO2. Subsequently, they are doped into the SiO2 oxide film formed by the oxidation of the silicide surface layer and the TiSi2+Ti5Si3 outer layer, thus optimizing the oxide film structure and inhibiting oxide film growth, thereby effectively improving the high-temperature oxidation resistance of the TiAl alloy.

[0023] 2. Unlike existing ultra-high temperature alloys such as Nb-Si alloys, which require temperatures as high as 1300℃ to prepare Hf and Al modified silicide coatings, this invention controls the heating and holding temperature of the diffusion embedding process to 900℃~1100℃, while adding appropriate amounts of Hf and Yb. Hf and Yb have larger atomic radii, which can form substitutional solid solutions in the coating during inward diffusion, increasing the degree of lattice distortion and thus providing more channels for the inward diffusion of Si. This promotes the inward diffusion of Si at low temperatures and avoids adverse effects on the TiAl alloy matrix structure while preparing the coating.

[0024] 3. The Si-Hf-Yb co-diffusion coating prepared by diffusion embedding in this invention has a metallurgical bond with the TiAl alloy substrate. The bonding force between the two was tested and confirmed by methods such as filing, scratching, and friction. The co-diffusion coating and the substrate exhibit very good bonding force, which avoids the co-diffusion coating from falling off and is beneficial to improving the high-temperature oxidation resistance of TiAl alloy.

[0025] 4. The Si-Hf-Yb co-diffusion coating preparation process of the present invention is simple, has good repeatability, and is easy to operate.

[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the preparation of Si-Hf-Yb co-diffusion coating on the surface of TiAl alloy according to the present invention.

[0028] Figure 2 This is a macroscopic view of the Si-Hf-Yb co-diffusion coating prepared on the surface of TiAl alloy in Example 1 of the present invention.

[0029] Figure 3 This is a SEM image of the surface morphology of the Si-Hf-Yb co-diffusion coating prepared on the surface of TiAl alloy in Example 1 of the present invention.

[0030] Figure 4 The image shows the XRD pattern of the Si-Hf-Yb co-diffusion coating prepared on the surface of TiAl alloy in Example 1 of this invention.

[0031] Figure 5 This is a cross-sectional BSE diagram of the Si-Hf-Yb co-diffusion coating prepared on the surface of TiAl alloy in Example 1 of the present invention. Detailed Implementation

[0032] Example 1

[0033] In this embodiment, the Si-Hf-Yb co-diffusion coating has a multilayer structure, consisting of, from the outside to the inside, a silicide surface layer rich in Hf and Yb, an outer TiSi2+Ti5Si3 layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and an inner TiAl2 layer; as shown below. Figure 1 As shown, the Si-Hf-Yb co-diffusion coating preparation method of this embodiment includes the following steps:

[0034] Step 1: Use 80# to 2000# SiC wet sandpaper to grind the TiAl alloy with a nominal composition of Ti-48Al-2Cr-2Nb (at.%) step by step, then put it into anhydrous ethanol for ultrasonic cleaning for 0.5h, and blow it dry to obtain the pretreated TiAl alloy.

[0035] Step 2: Prepare the infiltration agent by weighing the following powders according to the following mass percentages: Si 15%, Hf 10%, Yb2O3 2%, NaF 8%, Al2O3 65%. The powders of Si, Hf, Yb2O3, NaF and Al2O3 are all less than 200 mesh, and NaF is of analytical grade. Then, mix and grind them in a ball mill for 3 hours, and then dry them in an oven at 100℃ for 1 hour.

[0036] Step 3: Load the infiltration agent prepared in Step 2 into the crucible, then bury the pretreated TiAl alloy from Step 1 into the infiltration agent in the crucible and compact it. After compaction, the thickness of the infiltration agent covering the surface of the pretreated TiAl alloy in the crucible and the distance between the pretreated TiAl alloy and the bottom of the crucible should both be no less than 10 mm. Then cover the crucible and seal it with a high-temperature sealing mud prepared by mixing silica sol and Al2O3 at a mass concentration of 30% to 40% per 1L of silica sol with 1.5 kg of Al2O3. Then place it in a high-temperature resistance furnace.

[0037] Step 4: The crucible placed in the high-temperature resistance furnace in Step 3 is heated from room temperature to 1000℃ at a heating rate of 8.3℃ / min and held at that temperature for 6 hours to allow the diffusion agent to diffuse and embed the TiAl alloy. Then, the crucible is removed from the high-temperature resistance furnace and air-cooled to room temperature. The diffused and embedded TiAl alloy is then removed and ultrasonically cleaned in distilled water for 0.5 hours to remove residual diffusion agent powder. Finally, it is placed in a 100℃ oven and kept at that temperature for 1 hour to dry, thus obtaining a Si-Hf-Yb co-diffusion coating on the surface of the TiAl alloy.

[0038] Figure 2 This is a macroscopic image of the Si-Hf-Yb co-diffusion coating prepared on the TiAl alloy surface in this embodiment. Figure 2 It can be seen that the co-permeation coating remains intact on a macroscopic scale, with no obvious cracks or peeling.

[0039] Figure 3 This is a SEM image of the surface morphology of the Si-Hf-Yb co-diffusion coating prepared on the TiAl alloy surface in this embodiment. Figure 3 It can be seen that the surface of the co-permeation coating is relatively smooth, with traces of the sample pretreatment and polishing.

[0040] Figure 4 The image shows the XRD pattern of the Si-Hf-Yb co-diffusion coating prepared on the TiAl alloy surface in this embodiment. Figure 4 It can be seen that diffraction peaks of TiSi2 and Ti5Si3 are present in the figure.

[0041] Figure 5 This is a cross-sectional BSE image of the Si-Hf-Yb co-diffusion coating prepared on the TiAl alloy surface in this embodiment. Figure 5 It can be seen that the co-diffusion coating has a multi-layer structure. The coating can be divided into a thinner surface layer with a bright white structure, a light-colored outer layer, and a dark-colored inner layer. Furthermore, interdiffusion occurs between the outer and inner layers, forming a transition layer.

[0042] according to Figure 5 The components of each layer of the co-infiltrated coating were analyzed at sampling points (marked with X, 1-4), and the EDS results are shown in Table 1 below.

[0043] Table 1

[0044]

[0045] Table 1 shows that surface point 1 has a high content of Ti and Si, indicating it is a Ti silicide. Hf and Yb are mainly distributed in this layer, suggesting that the surface layer is a Hf- and Yb-rich silicide. Outer point 2 mainly contains Ti and Si. Based on the atomic ratio of Ti to Si, combined with... Figure 4 The XRD pattern shows that the outer layer is a mixture of TiSi2 and Ti5Si3; the inner layer at point 4 is an Al-rich layer with a Ti to Al atomic ratio close to 0.5, indicating a TiAl2 phase; the layer between the outer and inner layers is a transition layer. Figure 5 It can be seen that the transition layer is composed of strip-shaped TiSi2+Ti5Si3 and dark regions. The atomic ratio of Ti to Al in the dark region (point 3) is close to 0.5, but its Si content is higher than that of the inner layer. Thus, the phase composition of the dark region is Ti(Al,Si)2, that is, the composition of the transition layer is TiSi2+Ti5Si3+Ti(Al,Si)2.

[0046] Example 2

[0047] In this embodiment, the Si-Hf-Yb co-diffusion coating has a multilayer structure, consisting of, from the outside to the inside, a silicide surface layer rich in Hf and Yb, an outer TiSi2+Ti5Si3 layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and an inner TiAl2 layer; as shown below. Figure 1 As shown, the Si-Hf-Yb co-diffusion coating preparation method of this embodiment includes the following steps:

[0048] Step 1: Use 80# to 2000# SiC wet sandpaper to grind the TiAl alloy with a nominal composition of Ti-48Al-2Cr-2Nb (at.%) step by step, then put it into anhydrous ethanol for ultrasonic cleaning for 0.5h, and blow it dry to obtain the pretreated TiAl alloy.

[0049] Step 2: Prepare the infiltration agent by weighing the following powders according to the following mass percentages: Si 20%, Hf 5%, Yb2O3 2%, NaF 6%, Al2O3 67%. The powders of Si, Hf, Yb2O3, NaF and Al2O3 are all less than 200 mesh, and NaF is of analytical grade. Then, mix and grind them in a ball mill for 3 hours, and then dry them in an oven at 100℃ for 1 hour.

[0050] Step 3: Load the infiltration agent prepared in Step 2 into the crucible, then bury the pretreated TiAl alloy from Step 1 into the infiltration agent in the crucible and compact it. After compaction, the thickness of the infiltration agent covering the surface of the pretreated TiAl alloy in the crucible and the distance between the pretreated TiAl alloy and the bottom of the crucible should both be no less than 10 mm. Then cover the crucible and seal it with a high-temperature sealing mud prepared by mixing silica sol and Al2O3 at a mass concentration of 30% to 40% per 1L of silica sol with 1 kg of Al2O3. Then place it in a high-temperature resistance furnace.

[0051] Step 4: The crucible placed in the high-temperature resistance furnace in Step 3 is heated from room temperature to 1000℃ at a heating rate of 8.3℃ / min and held at that temperature for 4 hours to allow the diffusion agent to diffuse and embed the TiAl alloy. Then, the crucible is removed from the high-temperature resistance furnace and air-cooled to room temperature. The diffused and embedded TiAl alloy is then removed and ultrasonically cleaned in distilled water for 0.5 hours to remove residual diffusion agent powder. Finally, it is placed in a 100℃ oven and kept at that temperature for 1 hour to dry, thus obtaining a Si-Hf-Yb co-diffusion coating on the surface of the TiAl alloy.

[0052] Example 3

[0053] In this embodiment, the Si-Hf-Yb co-diffusion coating has a multilayer structure, consisting of, from the outside to the inside, a silicide surface layer rich in Hf and Yb, an outer TiSi2+Ti5Si3 layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and an inner TiAl2 layer; as shown below. Figure 1 As shown, the Si-Hf-Yb co-diffusion coating preparation method of this embodiment includes the following steps:

[0054] Step 1: Use 80# to 2000# SiC wet sandpaper to grind the TiAl alloy with a nominal composition of Ti-48Al-2Cr-2Nb (at.%) step by step, then put it into anhydrous ethanol for ultrasonic cleaning for 0.5h, and blow it dry to obtain the pretreated TiAl alloy.

[0055] Step 2: Prepare the infiltration agent by weighing the following powders according to the following mass percentages: Si 15%, Hf 10%, Yb2O3 3%, NaF 8%, Al2O3 64%. The powders of Si, Hf, Yb2O3, NaF and Al2O3 are all less than 200 mesh, and NaF is of analytical grade. Then, mix and grind them in a ball mill for 3 hours, and then dry them in an oven at 100℃ for 1 hour.

[0056] Step 3: Load the infiltration agent prepared in Step 2 into the crucible, then bury the pretreated TiAl alloy from Step 1 into the infiltration agent in the crucible and compact it. After compaction, the thickness of the infiltration agent covering the surface of the pretreated TiAl alloy in the crucible and the distance between the pretreated TiAl alloy and the bottom of the crucible should both be no less than 10 mm. Then cover the crucible and seal it with a high-temperature sealing mud prepared by mixing silica sol and Al2O3 at a mass concentration of 30% to 40% per 1L of silica sol with 1.2 kg of Al2O3. Then place it in a high-temperature resistance furnace.

[0057] Step 4: The crucible placed in the high-temperature resistance furnace in Step 3 is heated from room temperature to 1100℃ at a heating rate of 8.3℃ / min and held at that temperature for 6 hours to allow the diffusion agent to diffuse and embed the TiAl alloy. Then, the crucible is removed from the high-temperature resistance furnace and air-cooled to room temperature. The diffused and embedded TiAl alloy is then removed and ultrasonically cleaned in distilled water for 0.5 hours to remove residual diffusion agent powder. Finally, it is placed in a 100℃ oven and kept at that temperature for 1 hour to dry, thus obtaining a Si-Hf-Yb co-diffusion coating on the surface of the TiAl alloy.

[0058] Example 4

[0059] In this embodiment, the Si-Hf-Yb co-diffusion coating has a multilayer structure, consisting of, from the outside to the inside, a silicide surface layer rich in Hf and Yb, an outer TiSi2+Ti5Si3 layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and an inner TiAl2 layer; as shown below. Figure 1 As shown, the Si-Hf-Yb co-diffusion coating preparation method of this embodiment includes the following steps:

[0060] Step 1: Use 80# to 2000# SiC wet sandpaper to grind the TiAl alloy with a nominal composition of Ti-48Al-2Cr-2Nb (at.%) step by step, then put it in acetone for ultrasonic cleaning for 0.25h, and blow it dry to obtain the pretreated TiAl alloy;

[0061] Step 2: Prepare the infiltration agent by weighing the following powders according to the following mass percentages: Si 10%, Hf 15%, Yb2O3 2%, NaF 8%, Al2O3 65%. The powders of Si, Hf, Yb2O3, NaF and Al2O3 are all less than 200 mesh, and NaF is of analytical grade. Then, mix and grind them in a ball mill for 3 hours, and then dry them in an oven at 100℃ for 1 hour.

[0062] Step 3: Load the infiltration agent prepared in Step 2 into the crucible, then bury the pretreated TiAl alloy from Step 1 into the infiltration agent in the crucible and compact it. After compaction, the thickness of the infiltration agent covering the surface of the pretreated TiAl alloy in the crucible and the distance between the pretreated TiAl alloy and the bottom of the crucible should both be no less than 10 mm. Then cover the crucible and seal it with a high-temperature sealing mud prepared by mixing silica sol and Al2O3 at a mass concentration of 30% to 40% per 1L of silica sol with 1.5 kg of Al2O3. Then place it in a high-temperature resistance furnace.

[0063] Step 4: The crucible placed in the high-temperature resistance furnace in Step 3 is heated from room temperature to 1000℃ at a heating rate of 8.3℃ / min and held at that temperature for 6 hours to allow the diffusion agent to diffuse and embed the TiAl alloy. Then, the crucible is removed from the high-temperature resistance furnace and air-cooled to room temperature. The diffused and embedded TiAl alloy is then removed and ultrasonically cleaned in distilled water for 1 hour to remove residual diffusion agent powder. Finally, it is placed in a 100℃ oven and kept at that temperature for 1 hour to dry, thus obtaining a Si-Hf-Yb co-diffusion coating on the surface of the TiAl alloy.

[0064] Example 5

[0065] In this embodiment, the Si-Hf-Yb co-diffusion coating has a multilayer structure, consisting of, from the outside to the inside, a silicide surface layer rich in Hf and Yb, an outer TiSi2+Ti5Si3 layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and an inner TiAl2 layer; as shown below. Figure 1 As shown, the Si-Hf-Yb co-diffusion coating preparation method of this embodiment includes the following steps:

[0066] Step 1: Use 80# to 2000# SiC wet sandpaper to grind the TiAl alloy with the nominal composition Ti-48Al-2Cr-2Nb (at.%) step by step, then put it into anhydrous ethanol for ultrasonic cleaning for 0.3h, and blow it dry to obtain the pretreated TiAl alloy.

[0067] Step 2: According to the following mass percentage composition: Si 10%, Hf 10%, Yb2O3 1%, NaF 10%, Al2O3 69%, weigh out the powders of Si, Hf, Yb2O3, NaF and Al2O3, wherein the particle size of Si, Hf, Yb2O3 and Al2O3 powders is less than 200 mesh, and NaF is analytical grade. Then put them into a ball mill and grind them for 2 hours, and then put them in an oven at 100℃ for 0.5 hours to dry them, and prepare the infiltration agent.

[0068] Step 3: Load the infiltration agent prepared in Step 2 into the crucible, then bury the pretreated TiAl alloy from Step 1 into the infiltration agent in the crucible and compact it. After compaction, the thickness of the infiltration agent covering the surface of the pretreated TiAl alloy in the crucible and the distance between the pretreated TiAl alloy and the bottom of the crucible should both be no less than 10 mm. Then cover the crucible and seal it with a high-temperature sealing mud prepared by mixing silica sol and Al2O3 at a mass concentration of 30% to 40% per 1L of silica sol with 1.5 kg of Al2O3. Then place it in a high-temperature resistance furnace.

[0069] Step 4: The crucible placed in the high-temperature resistance furnace in Step 3 is heated from room temperature to 1000℃ at a heating rate of 8.3℃ / min and held at that temperature for 6 hours to allow the diffusion agent to diffuse and embed the TiAl alloy. Then, the crucible is removed from the high-temperature resistance furnace and air-cooled to room temperature. The diffused and embedded TiAl alloy is then removed and ultrasonically cleaned in distilled water for 0.5 hours to remove residual diffusion agent powder. Finally, it is placed in a 100℃ oven and kept at that temperature for 0.5 hours to dry, resulting in a Si-Hf-Yb co-diffusion coating on the surface of the TiAl alloy.

[0070] Example 6

[0071] In this embodiment, the Si-Hf-Yb co-diffusion coating has a multilayer structure, consisting of, from the outside to the inside, a silicide surface layer rich in Hf and Yb, an outer TiSi2+Ti5Si3 layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and an inner TiAl2 layer; as shown below. Figure 1 As shown, the Si-Hf-Yb co-diffusion coating preparation method of this embodiment includes the following steps:

[0072] Step 1: Use 80# to 2000# SiC wet sandpaper to grind the TiAl alloy with a nominal composition of Ti-48Al-2Cr-2Nb (at.%) step by step, then put it into anhydrous ethanol for ultrasonic cleaning for 0.5h, and blow it dry to obtain the pretreated TiAl alloy.

[0073] Step 2: According to the following mass percentage composition: Si 10%, Hf 10%, Yb2O3 5%, NaF 3%, Al2O3 72%, weigh out the powders of Si, Hf, Yb2O3, NaF and Al2O3, wherein the particle size of Si, Hf, Yb2O3 and Al2O3 powders is less than 200 mesh, and NaF is analytical grade. Then put them into a ball mill and grind them for 4 hours, and then put them in an oven at 100℃ for 0.75 hours to dry them, and prepare the infiltration agent.

[0074] Step 3: Load the infiltration agent prepared in Step 2 into the crucible, then bury the pretreated TiAl alloy from Step 1 into the infiltration agent in the crucible and compact it. After compaction, the thickness of the infiltration agent covering the surface of the pretreated TiAl alloy in the crucible and the distance between the pretreated TiAl alloy and the bottom of the crucible should both be no less than 10 mm. Then cover the crucible and seal it with a high-temperature sealing mud prepared by mixing silica sol and Al2O3 at a mass concentration of 30% to 40% per 1L of silica sol with 1.5 kg of Al2O3. Then place it in a high-temperature resistance furnace.

[0075] Step 4: The crucible placed in the high-temperature resistance furnace in Step 3 is heated from room temperature to 1000℃ at a heating rate of 8.3℃ / min and held at that temperature for 6 hours to allow the diffusion agent to diffuse and embed the TiAl alloy. Then, the crucible is removed from the high-temperature resistance furnace and air-cooled to room temperature. The diffused and embedded TiAl alloy is then removed and ultrasonically cleaned in distilled water for 0.75 hours to remove residual diffusion agent powder. Finally, it is placed in a 100℃ oven and kept at that temperature for 0.75 hours to dry, thus obtaining a Si-Hf-Yb co-diffusion coating on the surface of the TiAl alloy.

[0076] Example 7

[0077] In this embodiment, the Si-Hf-Yb co-diffusion coating has a multilayer structure, consisting of, from the outside to the inside, a silicide surface layer rich in Hf and Yb, an outer TiSi2+Ti5Si3 layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and an inner TiAl2 layer; as shown below. Figure 1 As shown, the Si-Hf-Yb co-diffusion coating preparation method of this embodiment includes the following steps:

[0078] Step 1: Use 80# to 2000# SiC wet sandpaper to grind the TiAl alloy with a nominal composition of Ti-48Al-2Cr-2Nb (at.%) step by step, then put it into anhydrous ethanol for ultrasonic cleaning for 0.25h, and blow it dry to obtain the pretreated TiAl alloy;

[0079] Step 2: Prepare the infiltration agent by weighing the following powders according to the following mass percentages: Si 15%, Hf 10%, Yb2O3 2%, NaF 8%, Al2O3 65%. The powders of Si, Hf, Yb2O3, NaF and Al2O3 are all less than 200 mesh, and NaF is of analytical grade. Then, mix and grind them in a ball mill for 3 hours, and then dry them in an oven at 100℃ for 1 hour.

[0080] Step 3: Load the infiltration agent prepared in Step 2 into the crucible, then bury the pretreated TiAl alloy from Step 1 into the infiltration agent in the crucible and compact it. After compaction, the thickness of the infiltration agent covering the surface of the pretreated TiAl alloy in the crucible and the distance between the pretreated TiAl alloy and the bottom of the crucible should both be no less than 10 mm. Then cover the crucible and seal it with a high-temperature sealing mud prepared by mixing silica sol and Al2O3 at a mass concentration of 30% to 40% per 1L of silica sol with 1.5 kg of Al2O3. Then place it in a high-temperature resistance furnace.

[0081] Step 4: The crucible placed in the high-temperature resistance furnace in Step 3 is heated from room temperature to 900℃ at a heating rate of 5℃ / min and held at that temperature for 8 hours to allow the diffusion agent to diffuse and embed the TiAl alloy. Then, the crucible is removed from the high-temperature resistance furnace and air-cooled to room temperature. The diffused and embedded TiAl alloy is then taken out and ultrasonically cleaned in distilled water for 0.5 hours to remove residual diffusion agent powder. Then, it is placed in a 100℃ oven and kept at that temperature for 1 hour to dry, thus obtaining a Si-Hf-Yb co-diffusion coating on the surface of the TiAl alloy.

[0082] Example 8

[0083] In this embodiment, the Si-Hf-Yb co-diffusion coating has a multilayer structure, consisting of, from the outside to the inside, a silicide surface layer rich in Hf and Yb, an outer TiSi2+Ti5Si3 layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and an inner TiAl2 layer; as shown below. Figure 1 As shown, the Si-Hf-Yb co-diffusion coating preparation method of this embodiment includes the following steps:

[0084] Step 1: Use 80# to 2000# SiC wet sandpaper to grind the TiAl alloy with a nominal composition of Ti-48Al-2Cr-2Nb (at.%) step by step, then put it in acetone for ultrasonic cleaning for 0.25h, and blow it dry to obtain the pretreated TiAl alloy;

[0085] Step 2: Prepare the infiltration agent by weighing the following powders according to the following mass percentages: Si 15%, Hf 10%, Yb2O3 2%, NaF 8%, Al2O3 65%. The powders of Si, Hf, Yb2O3, NaF and Al2O3 are all less than 200 mesh, and NaF is of analytical grade. Then, mix and grind them in a ball mill for 3 hours, and then dry them in an oven at 100℃ for 1 hour.

[0086] Step 3: Load the infiltration agent prepared in Step 2 into the crucible, then bury the pretreated TiAl alloy from Step 1 into the infiltration agent in the crucible and compact it. After compaction, the thickness of the infiltration agent covering the surface of the pretreated TiAl alloy in the crucible and the distance between the pretreated TiAl alloy and the bottom of the crucible should both be no less than 10 mm. Then cover the crucible and seal it with a high-temperature sealing mud prepared by mixing silica sol and Al2O3 at a mass concentration of 30% to 40% per 1L of silica sol with 1.5 kg of Al2O3. Then place it in a high-temperature resistance furnace.

[0087] Step 4: The crucible placed in the high-temperature resistance furnace in Step 3 is heated from room temperature to 1100℃ at a heating rate of 10℃ / min and held at that temperature for 3 hours to allow the diffusion agent to diffuse and embed the TiAl alloy. Then, the crucible is removed from the high-temperature resistance furnace and air-cooled to room temperature. The diffused and embedded TiAl alloy is then removed and ultrasonically cleaned in distilled water for 0.5 hours to remove residual diffusion agent powder. Finally, it is placed in a 100℃ oven and kept at that temperature for 1 hour to dry, thus obtaining a Si-Hf-Yb co-diffusion coating on the surface of the TiAl alloy.

[0088] Example 9

[0089] In this embodiment, the Si-Hf-Yb co-diffusion coating has a multilayer structure, consisting of, from the outside to the inside, a silicide surface layer rich in Hf and Yb, an outer TiSi2+Ti5Si3 layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and an inner TiAl2 layer; as shown below. Figure 1 As shown, the Si-Hf-Yb co-diffusion coating preparation method of this embodiment includes the following steps:

[0090] Step 1: Use 80# to 2000# SiC wet sandpaper to grind the TiAl alloy with a nominal composition of Ti-48Al-2Cr-2Nb (at.%) step by step, then put it in acetone for ultrasonic cleaning for 0.5 hours, and blow it dry to obtain the pretreated TiAl alloy;

[0091] Step 2: Prepare the infiltration agent by weighing the following powders according to the following mass percentages: Si 15%, Hf 10%, Yb2O3 2%, NaF 8%, Al2O3 65%. The powders of Si, Hf, Yb2O3, NaF and Al2O3 are all less than 200 mesh, and NaF is of analytical grade. Then, mix and grind them in a ball mill for 3 hours, and then dry them in an oven at 100℃ for 1 hour.

[0092] Step 3: Load the infiltration agent prepared in Step 2 into the crucible, then bury the pretreated TiAl alloy from Step 1 into the infiltration agent in the crucible and compact it. After compaction, the thickness of the infiltration agent covering the surface of the pretreated TiAl alloy in the crucible and the distance between the pretreated TiAl alloy and the bottom of the crucible should both be no less than 10 mm. Then cover the crucible and seal it with a high-temperature sealing mud prepared by mixing silica sol and Al2O3 at a mass concentration of 30% to 40% per 1L of silica sol with 1.5 kg of Al2O3. Then place it in a high-temperature resistance furnace.

[0093] Step 4: The crucible placed in the high-temperature resistance furnace in Step 3 is heated from room temperature to 900℃ at a heating rate of 8.3℃ / min and held at that temperature for 12 hours to allow the diffusion agent to diffuse and embed the TiAl alloy. Then, the crucible is removed from the high-temperature resistance furnace and air-cooled to room temperature. The diffused and embedded TiAl alloy is then removed and ultrasonically cleaned in distilled water for 0.5 hours to remove residual diffusion agent powder. Finally, it is placed in a 100℃ oven and kept at that temperature for 1 hour to dry, thus obtaining a Si-Hf-Yb co-diffusion coating on the surface of the TiAl alloy.

[0094] Example 10

[0095] In this embodiment, the Si-Hf-Yb co-diffusion coating has a multilayer structure, consisting of, from the outside to the inside, a silicide surface layer rich in Hf and Yb, an outer TiSi2+Ti5Si3 layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and an inner TiAl2 layer; as shown below. Figure 1 As shown, the Si-Hf-Yb co-diffusion coating preparation method of this embodiment includes the following steps:

[0096] Step 1: Use 80# to 2000# SiC wet sandpaper to grind the TiAl alloy with a nominal composition of Ti-48Al-2Cr-2Nb (at.%) step by step, then put it in acetone for ultrasonic cleaning for 0.3 hours, and blow it dry to obtain the pretreated TiAl alloy;

[0097] Step 2: Prepare the infiltration agent by weighing the following powders according to the following mass percentages: Si 15%, Hf 10%, Yb2O3 2%, NaF 8%, Al2O3 65%. The powders of Si, Hf, Yb2O3, NaF and Al2O3 are all less than 200 mesh, and NaF is of analytical grade. Then, mix and grind them in a ball mill for 3 hours, and then dry them in an oven at 100℃ for 1 hour.

[0098] Step 3: Load the infiltration agent prepared in Step 2 into the crucible, then bury the pretreated TiAl alloy from Step 1 into the infiltration agent in the crucible and compact it. After compaction, the thickness of the infiltration agent covering the surface of the pretreated TiAl alloy in the crucible and the distance between the pretreated TiAl alloy and the bottom of the crucible should both be no less than 10 mm. Then cover the crucible and seal it with a high-temperature sealing mud prepared by mixing silica sol and Al2O3 at a mass concentration of 30% to 40% per 1L of silica sol with 1.5 kg of Al2O3. Then place it in a high-temperature resistance furnace.

[0099] Step 4: The crucible placed in the high-temperature resistance furnace in Step 3 is heated from room temperature to 1000℃ at a heating rate of 8.3℃ / min and held at that temperature for 6 hours to allow the diffusion agent to diffuse and embed the TiAl alloy. Then, the crucible is removed from the high-temperature resistance furnace and air-cooled to room temperature. The diffused and embedded TiAl alloy is then removed and ultrasonically cleaned in distilled water for 0.5 hours to remove residual diffusion agent powder. Finally, it is placed in a 100℃ oven and kept at that temperature for 1 hour to dry, thus obtaining a Si-Hf-Yb co-diffusion coating on the surface of the TiAl alloy.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy, characterized in that, The Si-Hf-Yb co-diffusion coating has a multilayer structure, consisting of an Hf- and Yb-rich silicide surface layer, a TiSi2+Ti5Si3 outer layer, a TiSi2+Ti5Si3+Ti(Al,Si)2 transition layer, and a TiAl2 inner layer, from the outside to the inside. The method includes the following steps: Step 1: Grind the TiAl alloy step by step, then ultrasonically clean it in anhydrous ethanol or acetone, and dry it to obtain the pretreated TiAl alloy. Step 2: Weigh the powders of Si, Hf, Yb2O3, NaF and Al2O3, mix, grind and dry them to prepare the infiltration agent; Step 3: Put the carburizing agent prepared in Step 2 into the crucible, then embed the pretreated TiAl alloy from Step 1 into the carburizing agent in the crucible and compact it. Then cover the crucible and seal it with a high-temperature sealing mud made of silica sol and Al2O3 before placing it in a high-temperature resistance furnace. Step 4: Heat and maintain the temperature of the crucible placed in the high-temperature resistance furnace in Step 3, so that the diffusion agent diffuses and embeds the TiAl alloy, and a Si-Hf-Yb co-diffusion coating is obtained on the surface of the TiAl alloy.

2. The method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy according to claim 1, characterized in that, In step one, the TiAl alloy is polished step by step using 80# to 2000# SiC wet sandpaper, and the ultrasonic cleaning time is 0.25h to 0.5h.

3. The method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy according to claim 1, characterized in that, In step two, the powders are weighed according to the following mass percentages: Si 10%–20%, Hf 5%–15%, Yb2O3 1%–5%, NaF 3%–10%, with the balance being Al2O3; the particle size of the Si, Hf, Yb2O3, and Al2O3 powders is all less than 200 mesh, and the NaF is analytical grade.

4. The method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy according to claim 1, characterized in that, The grinding time in step two is 2h to 4h, and the drying temperature is 100℃ for 0.5h to 1h.

5. The method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy according to claim 1, characterized in that, In step three, the thickness of the infiltration agent covering the surface of the pretreated TiAl alloy in the crucible after compaction and the distance between the pretreated TiAl alloy and the bottom of the crucible are both not less than 10 mm.

6. The method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy according to claim 1, characterized in that, The mixing ratio of silica sol and Al2O3 in step three is as follows: 1 kg to 1.5 kg of Al2O3 is added to every 1 L of silica sol with a mass concentration of 30% to 40%.

7. The method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy according to claim 1, characterized in that, The heating and heat preservation process described in step four is as follows: heating from room temperature to 900℃ to 1100℃ at a heating rate of 5℃ / min to 10℃ / min and holding at that temperature for 3h to 12h, then removing the crucible from the high-temperature resistance furnace and air-cooling it to room temperature.

8. The method for preparing a Si-Hf-Yb co-diffusion coating on the surface of a TiAl alloy according to claim 7, characterized in that, Take out the TiAl alloy with Si-Hf-Yb co-diffusion coating on the surface of the crucible after it has been cooled to room temperature, put it in distilled water and ultrasonically clean it for 0.5h to 1h to remove residual infiltration agent powder, and then put it in a 100℃ oven and keep it at a temperature of 0.5h to 1h to dry it.

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