Methods to reduce cracks and holes in titanium alloy surface coatings and titanium alloy coatings

Abstract

This invention discloses a method for reducing cracks and pores in the coating of titanium alloy surfaces, comprising the following steps: 1) Immersing a pretreated titanium alloy in molten aluminum for plating, while simultaneously applying an alternating electromagnetic field during the plating process. After plating is completed, the alloy is removed and cooled, while simultaneously applying an alternating electromagnetic field during the cooling process, until the coating is completely cooled and solidified, yielding intermediate sample A; 2) Heating the intermediate sample A in a resistance furnace to a temperature of 780–820°C and holding it at that temperature for 25–35 min, then placing it in the intermediate sample A obtained in step 1) for diffusion and holding at that temperature for 12–14 h, followed by air cooling, yielding intermediate sample B; 3) Placing the intermediate sample B obtained in step 2) in a hot isostatic press for 10–30 min, followed by slow cooling in the furnace, yielding a coating on the titanium alloy surface; In step 3), the furnace temperature in the hot isostatic press is set to 800–1000°C, while simultaneously applying a pressure of 10–30 MPa.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy coating technology, and in particular to a method for reducing cracks and holes in the coating on the surface of titanium alloys, and a titanium alloy coating. Background Technology

[0002] With the rapid development of my country's aviation, aerospace, and military industries, the application of titanium alloy materials has attracted increasing attention. Titanium alloys possess excellent comprehensive mechanical properties and strong corrosion resistance, and are frequently used to manufacture aircraft landing gear, engine casings, compressor casings, and other components. While titanium alloys offer many advantages, they also have several drawbacks that limit their application. Titanium alloys have low hardness, making them prone to adhesive wear and abrasive wear. In high-temperature environments, the oxide film formed by their own oxidation is easily detached, failing to provide protection. This leads to a severe decline in mechanical properties, ultimately causing component failure and potentially serious accidents. Therefore, research on surface treatment of titanium alloys is of great significance.

[0003] Currently, various methods have been adopted to address the issue of cracks and voids easily forming on titanium alloy surface coatings. One method involves using an alternating magnetic field to assist in immersion plating. This involves forming a titanium-aluminum intermetallic compound between the titanium alloy substrate and the coating. Since this intermetallic compound possesses both metallic properties and the high melting point and high hardness of ceramic materials, it improves the hardness and wear resistance of the titanium alloy. However, the assisted alternating magnetic field cannot completely eliminate residual internal stress in the coating, and cracks and voids may still occur during the coating cooling process. Furthermore, the alternating magnetic field needs to be carefully controlled during immersion plating. If the plating time is too long and the magnetic field strength is too strong, the coating may not adhere to the titanium alloy surface. Conversely, if the plating time is too short and the magnetic field strength is too weak, the coating thickness will not meet the requirements. Therefore, it is necessary to combine the assisted immersion plating with other process improvements.

[0004] Hot isostatic pressing (HIP) is a process that enhances densification during the production of castings or components, thereby eliminating internal metallurgical defects and improving fatigue life. For example, Chinese patent CN 115821184 A describes a densification method for ZTi60 titanium alloy and its application. The method involves HIP treatment of ZTi60 titanium alloy at a heating temperature of 970–990°C, a holding time of 2.5–3 hours, and a pressure of 130–140 MPa. The patent document also states that conventional titanium alloy castings undergoing HIP treatment show significant improvements in internal quality (effective healing of metallurgical defects and microporous structures), which in turn affects the mechanical properties of the castings, slightly reducing strength, improving plasticity, and significantly increasing fatigue strength. However, the existing hot isostatic pressing process is mainly used for castings or cladding structures. Due to its high cost and the need for a sufficiently long processing time in the hot isostatic press to achieve the desired effect, the promotion of hot isostatic pressing in industrial applications is poor. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for reducing cracks and holes in the coating on the surface of titanium alloys, as well as the titanium alloy surface coating prepared by the method.

[0006] The objective of this invention is achieved through the following technical solution: A method for reducing cracks and voids in the coating of titanium alloy surfaces includes the following steps:

[0007] 1) The pretreated titanium alloy was immersed in molten aluminum for plating. An alternating electromagnetic field was applied during the plating process. After plating was completed, the alloy was removed and cooled. An alternating electromagnetic field was applied during the cooling process until the coating was completely cooled and solidified, thus obtaining intermediate sample A.

[0008] 2) Heat the sample to 780-820℃ in a resistance furnace and hold for 25-35 minutes. Then place the intermediate sample A obtained in step 1) into the furnace and hold for diffusion for 12-14 hours. After air cooling, the intermediate sample B is obtained.

[0009] 3) Place the intermediate sample B obtained in step 2) into a hot isostatic press and process for 10-30 minutes, then slowly cool it with the furnace to obtain a titanium alloy surface coating.

[0010] In step 3), the furnace temperature in the hot isostatic press is set to 800-1000℃, and a pressure of 10-30 MPa is applied simultaneously.

[0011] In step 3), one or a mixture of nitrogen and argon is used as the pressure medium in the hot isostatic press.

[0012] In step 1), the pretreatment steps for the titanium alloy are as follows: cut the titanium alloy into sheets, then polish and grind it, and then ultrasonically clean it for 8 to 12 minutes to obtain the pretreated titanium alloy.

[0013] During the ultrasonic cleaning process, the titanium alloy is ultrasonically cleaned sequentially using analytical grade acetone, sodium octadecyl sulfate, hydrochloric acid, and deionized water.

[0014] Step 1) Immersion plating involves melting an aluminum block at 740-780°C, then adding a covering agent and holding it at that temperature for 10-30 minutes to obtain molten aluminum. The pretreated titanium alloy is then immersed in the molten aluminum at 760°C for 1-3 minutes.

[0015] The covering agent is a chloride salt consisting of 50 wt% potassium chloride and 50 wt% sodium chloride;

[0016] In step 1), the alternating magnetic field strength applied during immersion plating is 30-40 mT, and the alternating magnetic field strength applied during cooling is 30-60 mT.

[0017] The titanium alloy is TA15 titanium alloy.

[0018] The present invention also provides a titanium alloy surface coating, which is prepared by the above method.

[0019] The present invention has the following advantages:

[0020] 1. The titanium alloy surface coating obtained by the preparation method of the present invention has good adhesion and is not easy to fall off. It not only improves the hardness, wear resistance and high temperature oxidation resistance of the alloy, but also improves the coating structure, with no obvious through cracks, and improves the hardness and wear resistance of the titanium alloy. It effectively solves the problems of easy coating fall-off and poor comprehensive performance in the prior art.

[0021] 2. During preparation, the pretreated titanium alloy is immersed in aluminum liquid and an alternating electromagnetic field. The alternating electromagnetic field can increase convection, resulting in a coating thickness of about 1.5 mm. This can improve the atomic diffusion rate between the coating and the substrate material, allowing them to bond better and preventing the coating material from cracking and peeling off during later use. It also improves the microstructure, refines the grains, and shortens the production cycle. Finally, high-temperature diffusion and heat preservation allow the coating to diffuse at high temperatures, refine the surface microstructure, and form a stable titanium-aluminum intermetallic compound.

[0022] 3. Hot-dip aluminum coating is a surface treatment method for titanium alloys. The titanium alloy parts are immersed in molten aluminum at a temperature above the melting point of pure aluminum, ensuring the titanium alloy does not melt. A series of thermochemical reactions occur at high temperatures, forming a very thin protective coating. High-temperature thermal diffusion of this coating refines the surface microstructure, forming a stable titanium-aluminum intercalary compound. This compound exhibits high hardness and wear resistance, and the outer surface readily forms a dense Al₂O₃ layer, preventing internal oxidation at high temperatures. This method improves the alloy's hardness, wear resistance, and resistance to high-temperature oxidation. Hot-dip aluminizing is a low-cost and simple-to-operate process for titanium alloys. The agitation effect of an applied alternating electromagnetic field induces a series of reactions between Al and Ti in situ during the plating process. Liquid Al and solid Ti atoms react at high temperatures to form titanium-aluminum intermetallic compounds, significantly shortening the plating time and production cycle. Furthermore, the agitation during coating solidification increases the atomic diffusion rate between the coating and the substrate material, leading to better bonding and preventing cracking and peeling of the coating material during later use. This effectively protects the base alloy and improves its resistance to high-temperature oxidation and surface wear resistance.

[0023] 4. Electromagnetic field plating: A power frequency alternating current is passed through the induction coil, generating an alternating magnetic field B. This magnetic field simultaneously induces a current J in the molten metal. The melt is then subjected to an electromagnetic volume force J×B, which acts as an electromagnetic stirrer. On one hand, the forced convection generated by electromagnetic stirring periodically changes the convection direction of the melt, making the convection more intense and increasing the diffusion rate between atoms. This significantly promotes the filling of the liquid metal into the substrate, inducing better bonding of Ti and Al atoms in situ, forming a more robust and continuous phase without obvious pores or cracks. Simultaneously, the shear force generated by the electromagnetic force breaks down dendrites, improving the microstructure and refining the grains. On the other hand, the alternating electromagnetic field changes the heat transfer and flow of the melt, altering the temperature distribution of the coating. Heat diffuses more evenly, enhancing the material exchange of the coating to a certain extent and significantly reducing the formation of pores and voids. It also shortens the plating time and accelerates the production cycle.

[0024] 5. Microcracks and voids are formed during the cooling process due to the significant difference in thermal expansion coefficients between the matrix and the diffusion layer phases, as well as the poor thermal conductivity of titanium alloys. This results in a large temperature gradient from the outside in during cooling, leading to directional solidification from the surface inwards, which is the main reason for crack propagation along grain boundaries. For electromagnetic field-assisted metal solidification, the alternating magnetic field of a specific intensity accelerates heat transfer within the coating, thus shortening the local solidification time. The interdendritic molten pool solidifies before it has time to precipitate. Furthermore, the solute in the coating is redistributed uniformly under forced convection caused by the magnetic field, promoting the melt to fill the voids generated during solidification shrinkage. This reduces the segregation of the solidified structure, which is beneficial for improving the coating's microstructure and reducing cracking.

[0025] 6. Hot isostatic pressing (HIP) can effectively eliminate internal pores and cracks in selected parts, thereby densifying the internal structure of the parts and obtaining fine grains through high-temperature treatment. At the same time, it greatly shortens the production cycle compared with traditional heat treatment. When the alternating magnetic field and HIP process are combined and applied to the preparation process of titanium alloy aluminum coating, the residual internal stress can be eliminated by HIP, and the remaining cracks after alternating magnetic field treatment can be repaired. Since the alternating magnetic field has already participated in the elimination of cracks and pores during the cooling process, the HIP treatment time does not need to be too long to achieve the desired effect, thus saving the cost of HIP. Attached Figure Description

[0026] Figure 1 This is a microstructure diagram of the titanium alloy surface coating obtained in Example 4.

[0027] Figure 2 The image shows the microstructure of the coating interface on the titanium alloy surface obtained in Comparative Example 1.

[0028] Figure 3 The image shows the microstructure of the coating interface on the titanium alloy surface obtained in Comparative Example 2.

[0029] Figure 4 The image shows the microstructure at the interface of the coating on the titanium alloy surface obtained in Comparative Example 3.

[0030] Figure 5 Microstructure of the coating interface on the titanium alloy surface obtained in Comparative Example 4

[0031] Figure 6 EDS analysis of the titanium alloy surface coating obtained in Example 4.

[0032] Figure 7 XRD analysis of the titanium alloy surface coating obtained in Example 4.

[0033] Figure 8 EDS analysis of the titanium alloy surface coating obtained in Comparative Example 1.

[0034] Figure 9 XRD analysis of the titanium alloy surface coating obtained in Comparative Example 2.

[0035] Figure 10 EDS analysis of the titanium alloy surface coating obtained in Comparative Example 2.

[0036] Figure 11 XRD analysis of the titanium alloy surface coating obtained in Comparative Example 2. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0038] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0039] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0040] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0041] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0042] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0043] Example 1: A method for reducing cracks and voids in the coating of titanium alloys, comprising the following steps:

[0044] 1) The pretreated titanium alloy was immersed in molten aluminum for plating. An alternating electromagnetic field was applied during the plating process. After plating was completed, the alloy was removed and cooled. An alternating electromagnetic field was applied during the cooling process until the coating was completely cooled and solidified, thus obtaining intermediate sample A.

[0045] 2) Heat the sample to 780-820℃ in a resistance furnace and hold for 25-35 minutes. Then place the intermediate sample A obtained in step 1) into the furnace and hold for diffusion for 12-14 hours. After air cooling, the intermediate sample B is obtained.

[0046] 3) Place the intermediate sample B obtained in step 2) into a hot isostatic press and process for 10-30 minutes, then slowly cool it with the furnace to obtain a titanium alloy surface coating.

[0047] In step 3), the furnace temperature in the hot isostatic press is set to 800-1000℃, and a pressure of 10-30 MPa is applied simultaneously.

[0048] In step 3), one or a mixture of nitrogen and argon is used as the pressure medium in the hot isostatic press.

[0049] In step 1), the pretreatment steps for the titanium alloy are as follows: cut the titanium alloy into sheets, then polish and grind it, and then ultrasonically clean it for 8 to 12 minutes to obtain the pretreated titanium alloy.

[0050] During the ultrasonic cleaning process, the titanium alloy is ultrasonically cleaned sequentially using analytical grade acetone, sodium octadecyl sulfate, hydrochloric acid, and deionized water.

[0051] Step 1) Immersion plating involves melting an aluminum block at 740-780°C, then adding a covering agent and holding it at that temperature for 10-30 minutes to obtain molten aluminum. The pretreated titanium alloy is then immersed in the molten aluminum at 760°C for 4-6 minutes.

[0052] The covering agent is a chloride salt consisting of 50 wt% potassium chloride and 50 wt% sodium chloride;

[0053] In step 1), the alternating magnetic field strength applied during immersion plating is 30-40 mT, and the alternating magnetic field strength applied during cooling is 30-60 mT.

[0054] The titanium alloy is TA15 titanium alloy.

[0055] Example 2: A method for reducing cracks and voids in the coating of titanium alloys, comprising the following steps:

[0056] 1) The pretreated titanium alloy was immersed in molten aluminum for plating. An alternating electromagnetic field was applied during the plating process. After plating was completed, the alloy was removed and cooled. An alternating electromagnetic field was applied during the cooling process until the coating was completely cooled and solidified, thus obtaining intermediate sample A.

[0057] 2) Heat the sample to 780℃ in a resistance furnace and hold for 25 minutes. Then place the intermediate sample A obtained in step 1) into the furnace and hold for diffusion for 12 hours. After air cooling, intermediate sample B is obtained.

[0058] 3) Place the intermediate sample B obtained in step 2) into a hot isostatic press and process for 10 minutes, then slowly cool it in the furnace to obtain a titanium alloy surface coating.

[0059] In step 3), the furnace temperature in the hot isostatic press is set to 800°C, and a pressure of 10 MPa is applied simultaneously.

[0060] In step 3), one or a mixture of nitrogen and argon is used as the pressure medium in the hot isostatic press.

[0061] In step 1), the pretreatment steps for the titanium alloy are as follows: cut the titanium alloy into sheets, then polish and grind it, and then ultrasonically clean it for 8 minutes to obtain the pretreated titanium alloy.

[0062] During the ultrasonic cleaning process, the titanium alloy is ultrasonically cleaned sequentially using analytical grade acetone, sodium octadecyl sulfate, hydrochloric acid, and deionized water.

[0063] Step 1) Immersion plating involves melting an aluminum block at 740°C, then adding a covering agent and holding it at that temperature for 10 minutes to obtain molten aluminum. The pretreated titanium alloy is then immersed in the molten aluminum at 760°C for 1 minute.

[0064] The covering agent is a chloride salt consisting of 50 wt% potassium chloride and 50 wt% sodium chloride;

[0065] In step 1), the alternating magnetic field strength applied during immersion plating is 30mT, and the alternating magnetic field strength applied during cooling is 30mT.

[0066] The titanium alloy is TA15 titanium alloy;

[0067] Example 3: A method for reducing cracks and voids in the coating of titanium alloys, comprising the following steps:

[0068] 1) The pretreated titanium alloy was immersed in molten aluminum for plating. An alternating electromagnetic field was applied during the plating process. After plating was completed, the alloy was removed and cooled. An alternating electromagnetic field was applied during the cooling process until the coating was completely cooled and solidified, thus obtaining intermediate sample A.

[0069] 2) Heat the sample to 820℃ in a resistance furnace and hold for 35 minutes. Then place the intermediate sample A obtained in step 1) into the furnace and hold for diffusion for 14 hours. After air cooling, intermediate sample B is obtained.

[0070] 3) Place the intermediate sample B obtained in step 2) into a hot isostatic press and process for 30 minutes, then slowly cool it in the furnace to obtain a titanium alloy surface coating.

[0071] In step 3), the furnace temperature in the hot isostatic press is set to 1000°C, and a pressure of 30 MPa is applied simultaneously.

[0072] In step 3), one or a mixture of nitrogen and argon is used as the pressure medium in the hot isostatic press.

[0073] In step 1), the pretreatment steps for the titanium alloy are as follows: cut the titanium alloy into sheets, then polish and grind it, and then ultrasonically clean it for 12 minutes to obtain the pretreated titanium alloy.

[0074] During the ultrasonic cleaning process, the titanium alloy is ultrasonically cleaned sequentially using analytical grade acetone, sodium octadecyl sulfate, hydrochloric acid, and deionized water.

[0075] Step 1) Immersion plating involves melting an aluminum block at 780°C, then adding a covering agent and holding it at that temperature for 30 minutes to obtain molten aluminum. The pretreated titanium alloy is then immersed in the molten aluminum at 760°C for 3 minutes.

[0076] The covering agent is a chloride salt consisting of 50 wt% potassium chloride and 50 wt% sodium chloride;

[0077] In step 1), the alternating magnetic field strength applied during immersion plating is 40 mT, and the alternating magnetic field strength applied during cooling is 60 mT.

[0078] The titanium alloy is TA15 titanium alloy;

[0079] Example 4: A method for reducing cracks and voids in the coating of titanium alloys, comprising the following steps:

[0080] 1) The pretreated titanium alloy was immersed in molten aluminum for plating. An alternating electromagnetic field was applied during the plating process. After plating was completed, the alloy was removed and cooled. An alternating electromagnetic field was applied during the cooling process until the coating was completely cooled and solidified, thus obtaining intermediate sample A.

[0081] 2) Heat the sample to 780℃ in a resistance furnace and hold for 25 minutes. Then place the intermediate sample A obtained in step 1) into the furnace and hold for diffusion for 12 hours. After air cooling, intermediate sample B is obtained.

[0082] 3) Place the intermediate sample B obtained in step 2) into a hot isostatic press and process for 20 minutes, then slowly cool it in the furnace to obtain a titanium alloy surface coating.

[0083] In step 3), the furnace temperature in the hot isostatic press is set to 800°C, and a pressure of 30 MPa is applied simultaneously.

[0084] In step 3), nitrogen is used as the pressure medium in the hot isostatic press.

[0085] In step 1), the pretreatment steps for the titanium alloy are as follows: cut the titanium alloy into 3mm thick sheets, then polish and grind them, and then ultrasonically clean them for 8 minutes to obtain the pretreated titanium alloy.

[0086] During the ultrasonic cleaning process, the titanium alloy is ultrasonically cleaned sequentially using analytical grade acetone, sodium octadecyl sulfate, hydrochloric acid, and deionized water.

[0087] Step 1) Immersion plating involves melting an aluminum block at 740°C, then adding a covering agent and holding it at that temperature for 10 minutes to obtain molten aluminum. The pretreated titanium alloy is then immersed in the molten aluminum at 760°C for 1 minute.

[0088] The covering agent is a chloride salt consisting of 50 wt% potassium chloride and 50 wt% sodium chloride;

[0089] In step 1), the alternating magnetic field strength applied during immersion plating is 30 mT, and the alternating magnetic field strength applied during cooling is 35 mT.

[0090] The titanium alloy is TA15 titanium alloy.

[0091] Comparative Example 1: A titanium alloy surface coating was prepared using the following steps;

[0092] 1) Cut TA15 titanium alloy into 3mm thick sheets, then polish, grind, and ultrasonically clean for 8 minutes to obtain pretreated titanium alloy.

[0093] 2) Melt the aluminum block at 740℃, then add a chloride salt with 50wt% potassium chloride and 50wt% sodium chloride as a covering agent and keep it at the temperature for 10min to obtain aluminum liquid. Then immerse the pretreated titanium alloy obtained in step 1) in the aluminum liquid at 760℃ for 1min, while applying an alternating electromagnetic field of 30mT to form a titanium-aluminum intercompound. During the cooling process, apply an alternating magnetic field of 35mT to obtain an intermediate sample.

[0094] 3) Heat the resistance furnace to 780℃ and hold for 25 minutes. Then place the intermediate sample obtained in step 2) into the furnace and hold for 12 hours for diffusion. After air cooling, the titanium alloy surface coating is obtained.

[0095] Comparative Example 2: A titanium alloy surface coating was prepared using the following steps;

[0096] 1) Cut TA15 titanium alloy into 3mm thick sheets, then polish, grind, and ultrasonically clean for 10 minutes to obtain pretreated titanium alloy.

[0097] 2) Melt the aluminum block at 760℃, then add a chloride salt with 50wt% potassium chloride and 50wt% sodium chloride as a covering agent and keep it at the temperature for 20min to obtain aluminum liquid. Then immerse the pretreated titanium alloy obtained in step 1) in the aluminum liquid for 2min and air cool to obtain an intermediate sample.

[0098] 3) Heat the resistance furnace to 800℃ and hold for 30 minutes. Then place the intermediate sample obtained in step 2) into the furnace and hold for diffusion for 13 hours. Air cool to obtain a titanium alloy surface coating.

[0099] Comparative Example 3: A titanium alloy surface coating was prepared using the following steps;

[0100] 1) Cut TA15 titanium alloy into 3mm thick sheets, then polish, grind, and ultrasonically clean for 8 minutes to obtain pretreated titanium alloy.

[0101] 2) Melt the aluminum block at 740℃, then add a chloride salt with 50wt% potassium chloride and 50wt% sodium chloride as a covering agent and keep it at the temperature for 10min to obtain aluminum liquid. Then immerse the pretreated titanium alloy obtained in step 1) in the aluminum liquid at 760℃ for 1min, while applying an alternating electromagnetic field of 30mT to form a titanium-aluminum intercompound. Air cool to obtain intermediate sample A.

[0102] 3) Heat the resistance furnace to 780℃ and hold for 25 minutes. Then place the intermediate sample obtained in step 2) into the furnace and keep it at the temperature for 12 hours. After air cooling, the intermediate sample B is obtained.

[0103] 4) Place intermediate sample B in a hot isostatic press for 20 minutes. Set the furnace temperature to 800℃ and apply a pressure of 30 MPa. Cool slowly with the furnace to obtain a titanium alloy surface coating.

[0104] Comparative Example 4: A titanium alloy surface coating was prepared using the following steps;

[0105] 1) Cut TA15 titanium alloy into 3mm thick sheets, then polish, grind, and ultrasonically clean for 8 minutes to obtain pretreated titanium alloy.

[0106] 2) Melt the aluminum block at 740℃, then add a chloride salt with 50wt% potassium chloride and 50wt% sodium chloride as a covering agent and keep it at the temperature for 10min to obtain aluminum liquid. Then immerse the pretreated titanium alloy obtained in step 1) in the aluminum liquid at 760℃ for 1min, take it out and cool it. Apply an alternating magnetic field of 35mT during the cooling process to obtain intermediate sample A.

[0107] 3) Heat the resistance furnace to 780℃ and hold for 25 minutes. Then place the intermediate sample obtained in step 2) into the furnace and keep it at the temperature for 12 hours. After air cooling, the intermediate sample B is obtained.

[0108] 4) Place intermediate sample B in a hot isostatic press for 20 minutes. Set the furnace temperature to 800℃ and apply a pressure of 30 MPa. Cool slowly with the furnace to obtain a titanium alloy surface coating.

[0109] Comparative Example 5: A titanium alloy surface coating was prepared using the following steps;

[0110] 1) Cut TA15 titanium alloy into 3mm thick sheets, then polish, grind, and ultrasonically clean for 8 minutes to obtain pretreated titanium alloy.

[0111] 2) Melt the aluminum block at 740℃, then add a chloride salt with 50wt% potassium chloride and 50wt% sodium chloride as a covering agent and keep it at the temperature for 10min to obtain aluminum liquid. Then immerse the pretreated titanium alloy obtained in step 1) in the aluminum liquid at 760℃ for 1min, while applying an alternating electromagnetic field of 65mT to form a titanium-aluminum intercompound. Air cool to obtain intermediate sample A.

[0112] 3) Heat the resistance furnace to 780℃ and hold for 25 minutes. Then place the intermediate sample obtained in step 2) into the furnace and keep it at the temperature for 12 hours. After air cooling, the intermediate sample B is obtained.

[0113] 4) The intermediate sample B was placed in a hot isostatic press and treated for 20 minutes. The furnace temperature was set to 800℃, and a pressure of 30 MPa was applied. The sample was then slowly cooled in the furnace to obtain a coating on the titanium alloy surface. In this comparative example, a 65 mT alternating magnetic field was used for immersion plating, which failed to form a uniform coating structure on the titanium alloy surface that met the required thickness.

[0114] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of reducing coating cracks and voids on a titanium alloy surface, characterized by, It includes the following steps: 1) The pretreated titanium alloy was immersed in molten aluminum for plating. An alternating electromagnetic field was applied during the plating process. After plating was completed, the alloy was removed and cooled. An alternating electromagnetic field was applied during the cooling process until the coating was completely cooled and solidified, thus obtaining intermediate sample A. 2) Heat the sample to 780-820℃ in a resistance furnace and hold for 25-35 minutes. Then place the intermediate sample A obtained in step 1) into the furnace and hold for diffusion for 12-14 hours. After air cooling, intermediate sample B is obtained. 3) Place the intermediate sample B obtained in step 2) into a hot isostatic press and process for 10-30 minutes, then slowly cool it with the furnace to obtain a titanium alloy surface coating. In step 3), the furnace temperature in the hot isostatic press is set to 800-1000℃, and a pressure of 10-30MPa is applied simultaneously.

2. The method of claim 1, wherein: In step 3), nitrogen or a mixture of two of the following gases is used as the pressure medium in the hot isostatic press:

3. The method for reducing surface coating cracks and porosity of titanium alloys according to claim 1, characterized in that: In step 1), the pretreatment steps for the titanium alloy are as follows: cut the titanium alloy into sheets, then polish and grind them, and then ultrasonically clean them for 8 to 12 minutes to obtain the pretreated titanium alloy.

4. The method for reducing surface coating cracks and porosity of titanium alloys according to claim 3, characterized in that: During the ultrasonic cleaning process, the titanium alloy was ultrasonically cleaned sequentially using analytical grade acetone, sodium octadecyl sulfate, hydrochloric acid, and deionized water.

5. The method for reducing surface coating cracks and porosity of titanium alloys according to claim 1, characterized in that: Step 1) Immersion plating involves melting an aluminum block at a temperature of 740–780°C, then adding a covering agent and holding it at that temperature for 10–30 minutes to obtain molten aluminum. The pretreated titanium alloy is then immersed in the molten aluminum at 760°C for 1–3 minutes.

6. The method for reducing surface coating cracks and porosity of titanium alloys according to claim 5, characterized in that: The covering agent is a chloride salt consisting of 50 wt% potassium chloride and 50 wt% sodium chloride.

7. The method for reducing surface coating cracks and porosity of titanium alloys according to claim 1, characterized in that: In step 1), the alternating magnetic field strength applied during immersion plating is 30-40 mT, and the alternating magnetic field strength applied during cooling is 30-60 mT.

8. The method for reducing surface coating cracks and porosity of titanium alloys according to claim 1, characterized in that: The titanium alloy is TA15 titanium alloy.

9. A coating on the surface of a titanium alloy, characterized in that: It is prepared by any one of claims 1-8.

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