Method for connecting Bi-In-Sn liquid metal coating and titanium alloy matrix

Abstract

The invention discloses a method for connecting a Bi-In-Sn liquid metal coating and a titanium alloy matrix, and belongs to the technical field of liquid metal application, and the method comprises the following steps: carrying out mechanical polishing on a to-be-connected surface of the titanium alloy matrix to remove an oxide layer and pollutants; the pretreated to-be-connected area is completely wrapped with a low-melting-point Bi-In-Sn alloy; the Bi-In-Sn alloy is heated to 700 DEG C in the inert gas protection atmosphere, heat preservation is conducted for 6 hours, the Bi-In-Sn alloy is molten and fully interdiffused with a titanium alloy matrix, and a compact and continuous diffusion bonding layer is formed; and after cooling, redundant alloy is removed, and then the Bi-based coating is prepared on the diffusion bonding layer through coating, spraying or electroplating. According to the method, the bonding strength of the Bi-based coating and the titanium alloy matrix can be remarkably improved, the interface is free of cracks, holes and other defects, the process stability is high, the adaptability is high, and the application requirements in the fields of biomedical implants, electronic heat management, flexible electronics and the like can be met.

Description

Technical Field

[0001] This invention relates to the field of liquid metal application technology, and in particular to a method for connecting a Bi-In-Sn liquid metal coating to a titanium alloy substrate. Background Technology

[0002] Bi-based cryogenic liquid metals, with their low melting point, excellent fluidity, and good biocompatibility, have shown significant application potential in fields such as thermal management, flexible electronics, and biomedical coatings. Among them, titanium alloys, due to their high strength, strong corrosion resistance, and biocompatibility, have become the core matrix material for biomedical implants and high-end structural components. Achieving a firm bond between Bi-based cryogenic liquid metal coatings and titanium alloy substrates is a key requirement for promoting the implementation of these technologies.

[0003] However, common coating preparation methods such as thermal spraying, electroplating, and physical vapor deposition (PVD) cannot effectively bond Bi-based liquid metals to titanium alloys. Titanium alloys readily form a stable oxide layer with significantly different physicochemical properties from Bi-based alloys, resulting in poor wettability. Furthermore, liquid Bi has limited dissolving power for titanium, and conventional bonding methods cannot form an effective metallurgical bond or diffusion layer at the interface, ultimately leading to easy coating peeling and low service reliability. Existing coating preparation methods cannot simultaneously ensure coating integrity and bonding effectiveness. High-temperature processes such as thermal spraying require heating to temperatures far exceeding the melting point of Bi-based alloys, easily causing the Bi-based coating to melt, deform, and lose its original function. Low-temperature processes such as electroplating, while avoiding coating damage, cannot penetrate the stable oxide layer on the titanium alloy surface, making it difficult to achieve effective deposition of Bi-based alloys on the substrate. Even if bonding is achieved through conventional methods, defects such as cracks and pores easily arise at the interface due to oxidation and insufficient element diffusion, further weakening the bonding strength between the coating and the substrate, failing to meet the stringent requirements for coating stability in thermal management, biomedical, and other applications.

[0004] Therefore, there is an urgent need to provide a method for joining Bi-based cryogenic liquid metal coatings to titanium alloy substrates that can take into account high adhesion, process feasibility, and interface integrity. Summary of the Invention

[0005] The purpose of this invention is to provide a method for joining a Bi-In-Sn liquid metal coating to a titanium alloy substrate, in order to solve the above-mentioned problems.

[0006] This invention provides a method for bonding a Bi-In-Sn liquid metal coating to a titanium alloy substrate, comprising the following steps: S1. Substrate pretreatment: The surfaces of the titanium alloy substrate to be joined are mechanically ground to completely remove the oxide layer and contaminants on the surfaces to be joined, so as to obtain a fresh and active metal surface. S2. Assembly: A low-melting-point Bi-In-Sn alloy is used to completely wrap the area to be joined of the titanium alloy substrate after the pretreatment in step S1, and to ensure that the low-melting-point Bi-In-Sn alloy is in full contact with the surface to be joined. S3. Diffusion bonding: The sample assembled in step S2 is placed in an inert gas protective atmosphere, heated to 700°C, and kept at that temperature for 4-8 hours to melt the low-melting-point Bi-In-Sn alloy. The molten Bi-In-Sn alloy and the fresh metal surface of the titanium alloy substrate undergo sufficient interdiffusion to form a diffusion bonding layer. S4. Post-processing: Cool the sample that has undergone diffusion bonding in step S3 to room temperature, and then remove the excess Bi-In-Sn alloy covering the outside of the area to be bonded in the titanium alloy matrix. S5. Coating preparation: A Bi-based coating is prepared on the diffusion bonding layer region formed after step S4 by coating, spraying or electroplating.

[0007] Preferably, in the above-mentioned method for connecting a Bi-In-Sn liquid metal coating to a titanium alloy substrate, the heat preservation time in step S3 is 6 hours.

[0008] Preferably, in the above-mentioned method for connecting a Bi-In-Sn liquid metal coating to a titanium alloy substrate, the inert gas in step S3 is argon.

[0009] Preferably, in the above-mentioned method for connecting a Bi-In-Sn liquid metal coating to a titanium alloy substrate, the composition of the Bi-based coating in step S5 is the same as or different from the composition of the low-melting-point Bi-In-Sn alloy in step S2.

[0010] Preferably, in the above-mentioned method for connecting a Bi-In-Sn liquid metal coating to a titanium alloy substrate, the diffusion bonding layer formed in step S3 has a dense and continuous structure, and there are no cracks or pores in the diffusion bonding layer. In the diffusion bonding layer, Ti, Bi, In and Sn elements interdiffusion occur.

[0011] Preferably, in the above-mentioned method for connecting a Bi-In-Sn liquid metal coating to a titanium alloy substrate, the substrate pretreatment in step 1) further includes: cleaning the surface to be connected after mechanical grinding to remove grinding residue.

[0012] Therefore, the present invention employs the above-described method for connecting a Bi-In-Sn liquid metal coating to a titanium alloy substrate, which has the following beneficial effects: (1) By first breaking the oxide layer and then using high-temperature diffusion to form a metallurgical bonding layer, the problem of poor wettability and weak bonding force between Bi-based alloys and titanium alloys is completely solved. Through mechanical grinding pretreatment, the oxide layer and contaminants on the surface of the titanium alloy to be joined can be completely removed, exposing a fresh and active metal surface, clearing obstacles for subsequent element diffusion. The subsequent diffusion bonding process at 700℃ uses molten Bi-In-Sn alloy as a medium to promote the full interdiffusion of Bi, In, Sn elements with Ti elements in the titanium alloy matrix, and finally forms a stable metallurgical bonding layer at the interface. The final bonding layer has a dense and continuous microstructure without defects such as cracks and pores, and the Ti, Bi, In, and Sn elements diffuse evenly. This high-quality interface can not only further enhance the bonding stability between the coating and the substrate, but also isolate the substrate from the erosion of the external medium, effectively avoiding the risk of coating peeling during service, and greatly improving the structural stability and service life of the product.

[0013] (2) The diffusion bonding temperature of this invention is lower than the phase transformation temperature of titanium alloys, while ensuring that the Bi-In-Sn alloy is completely melted and elements diffuse, thus avoiding damage to the coating raw materials caused by high temperature. At the same time, the inert gas protective atmosphere can isolate air and prevent secondary oxidation of the titanium alloy matrix and Bi-based alloy during diffusion, ensuring the quality of interface bonding. The entire process is clear, and the required equipment is all conventional industrial equipment. Parameters such as heating temperature and holding time are easy to control, have good repeatability, do not require extreme process conditions, and are easy to scale up for mass production, solving the problems of complex processes and difficulty in mass production in existing technologies.

[0014] (3) In the coating preparation stage, this invention allows the Bi-based coating composition to be the same as or different from the Bi-In-Sn alloy used for diffusion bonding. In the biomedical field, a highly biocompatible Bi-In-Sn coating can be selected for antibacterial or radiation shielding functions of implants; in the thermal management field, a highly thermally conductive Bi-Zn coating can be selected to improve heat dissipation efficiency. This compositional flexibility breaks the limitation of coating composition being bound to the bonding medium, enabling the technology to adapt to the functional requirements of different fields such as thermal management, flexible electronics, and biomedicine, and expanding the boundaries of the synergistic application of Bi-based cryogenic liquid metal and titanium alloy.

[0015] 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

[0016] Figure 1 This is a flowchart illustrating the process of connecting the Bi-based coating to the titanium alloy substrate according to the present invention. Figure 2 This is an optical image showing the connection between the Bi-In-Sn coating and the Ti-6Al-4V substrate of the present invention, wherein a) is the connection sample; b) is the connection interface; Figure 3 The images show the microscopic connection between the Bi-In-Sn coating and the Ti-6Al-4V substrate of the present invention, where a) is a SEM image and b) is an EDX image. Detailed Implementation

[0017] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0018] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0019] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0020] Example like Figure 1-2 As shown, the bonding process between the Bi-based cryogenic liquid metal coating and the Ti-6Al-4V titanium alloy substrate is as follows: This embodiment aims to achieve a high bonding strength between the Bi-based cryogenic liquid metal coating and the Ti-6Al-4V titanium alloy substrate. Appropriate materials and equipment are selected based on actual process requirements to ensure that the entire bonding process is operable and verifiable.

[0021] First, the substrate is pretreated. During the operation, the Ti-6Al-4V substrate surface to be joined is first coarsely ground with 80-grit metallographic sandpaper to quickly remove the oxide scale and surface contaminants formed by long-term exposure. Then, 400-grit, 800-grit, and 1200-grit metallographic sandpaper are used for fine grinding until the substrate surface shows a uniform metallic luster without obvious scratches, confirming that the original oxide layer on the substrate surface has been completely removed, exposing a fresh and active metal surface. Finally, the surface to be joined after grinding is gently wiped with a lint-free cloth soaked in anhydrous ethanol to clean up any residual metal debris and prevent debris from adhering to the substrate surface and becoming a source of interface defects for subsequent diffusion bonding.

[0022] After completing the matrix pretreatment, the assembly step is carried out. The Bi-In-Sn alloy is laid flat on the area to be joined of the pretreated Ti-6Al-4V matrix. The assembled sample is placed in a graphite mold, and the alloy block is gently pressed with a graphite press block to make the alloy block fit tightly with the matrix surface to be joined. This ensures that the molten Bi-In-Sn alloy can fully contact the fresh surface of the matrix during the subsequent diffusion bonding process, creating favorable conditions for element interdiffusion.

[0023] After assembly, a diffusion bonding step is performed. Under an argon atmosphere, the furnace temperature is raised to 700°C at a heating rate of 10°C / min. Once the furnace temperature reaches 700°C, it is maintained at this temperature for 6 hours. During the holding process, argon gas is continuously introduced to ensure the stability of the inert atmosphere inside the furnace. During this process, the Bi-In-Sn alloy completely melts due to reaching its melting point. The molten Bi, In, and Sn elements fully contact and interdiffused with the fresh Ti elements exposed in the Ti-6Al-4V matrix, gradually forming a diffusion bonding layer at the interface.

[0024] After diffusion bonding is completed, a post-processing step is performed. The sample, cooled to room temperature, is taken out. At this time, a solidified Bi-In-Sn alloy layer can be observed on the surface of the Ti-6Al-4V substrate to be bonded. A diffusion bonding layer has been formed at the interface with the substrate, while the surface part is excess alloy that has not participated in interdiffusion. Using a mechanical peeling method, the excess Bi-In-Sn alloy on the surface is gently scraped off along the substrate surface. After scraping off the excess alloy, the surface of the diffusion bonding layer is lightly polished with sandpaper to remove residual alloy debris and surface burrs, making the surface of the diffusion bonding layer smooth and providing good substrate conditions for subsequent coating preparation.

[0025] Finally, the coating preparation step is performed. Alloy powder with the same composition as the Bi-In-Sn alloy used for diffusion bonding is selected, and a coating is prepared on the surface of the diffusion bonding layer by plasma spraying.

[0026] like Figure 3 As shown, the performance of the prepared coating sample was tested. SEM observation of the microstructure of the diffusion bonding layer revealed a continuous and dense structure without cracks, pores, or other defects. Elemental analysis using EDX showed that Ti diffused from the Ti-6Al-4V matrix into the diffusion bonding layer, while Bi, In, and Sn diffused from the molten alloy into the matrix, demonstrating sufficient interdiffusion of the four elements and further verifying the metallurgical bonding characteristics of the diffusion bonding layer.

[0027] Therefore, it can be seen that the present invention adopts the above-mentioned method for joining Bi-In-Sn liquid metal coating and titanium alloy substrate. By first removing the oxide layer and then using high-temperature diffusion to form a metallurgical bonding layer, the problems of poor wettability and weak bonding force between Bi-based alloy and titanium alloy are completely solved. Through mechanical grinding pretreatment, the oxide layer and contaminants on the surface of the titanium alloy to be joined can be completely removed, exposing a fresh and active metal surface, clearing obstacles for subsequent element diffusion. The subsequent diffusion bonding process at 700°C uses molten Bi-In-Sn alloy as a medium to promote the full interdiffusion of Bi, In, Sn elements and Ti elements in the titanium alloy substrate, and finally forms a stable metallurgical bonding layer at the interface. The final bonding layer has a dense and continuous microstructure, without defects such as cracks and pores, and the Ti, Bi, In, and Sn elements are diffused uniformly. This high-quality interface can not only further enhance the bonding stability between the coating and the substrate, but also isolate the substrate from the erosion of the substrate by the external medium, effectively avoiding the risk of coating peeling during service, and greatly improving the structural stability and service life of the product.

[0028] The diffusion bonding temperature of this invention is lower than the phase transformation temperature of titanium alloys, yet it ensures complete melting of the Bi-In-Sn alloy and element diffusion, avoiding damage to the coating material from high temperatures. Simultaneously, the inert gas protective atmosphere isolates the titanium alloy matrix from air, preventing secondary oxidation between the titanium alloy matrix and the Bi-based alloy during diffusion, thus guaranteeing the quality of the interface bonding. The entire process is clear, requiring only conventional industrial equipment. Parameters such as heating temperature and holding time are easily controlled, exhibiting good repeatability. It requires no extreme process conditions, facilitating large-scale production and solving the problems of complex processes and difficulty in mass production inherent in existing technologies. In the coating preparation stage, this invention allows the Bi-based coating composition to be the same as or different from the Bi-In-Sn alloy used for diffusion bonding. In the biomedical field, a highly biocompatible Bi-In-Sn coating can be selected for antibacterial or radiation shielding functions in implants; in the thermal management field, a highly thermally conductive Bi-Zn coating can be used to improve heat dissipation efficiency. This compositional flexibility breaks the limitation of binding coating components to the bonding medium, enabling the technology to adapt to the functional requirements of different fields such as thermal management, flexible electronics, and biomedicine, and expanding the boundaries of the synergistic application of Bi-based cryogenic liquid metals and titanium alloys.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for joining a Bi-In-Sn liquid metal coating to a titanium alloy substrate, characterized by, The method comprises the following steps: S1, substrate pretreatment: mechanically polishing the surface to be connected of the titanium alloy substrate to completely remove the oxide layer and contaminants on the surface to be connected, and obtain a fresh and active metal surface; S2, assembly: using a low-melting-point Bi-In-Sn alloy to completely wrap the connecting area of the titanium alloy substrate pretreated in step S1, and ensuring that the low-melting-point Bi-In-Sn alloy is in full contact with the surface to be connected; S3, diffusion bonding: placing the sample assembled in step S2 in an inert gas protective atmosphere, heating to 700 DEG C, and keeping for 4-8 hours, so that the low-melting-point Bi-In-Sn alloy melts, and the molten Bi-In-Sn alloy and the fresh metal surface of the titanium alloy substrate fully interdiffuse to form a diffusion bonding layer; S4, post-treatment: cooling the sample diffusion bonded in step S3 to room temperature, and then removing the excess Bi-In-Sn alloy covering the outside of the connecting area of the titanium alloy substrate; S5, coating preparation: preparing a Bi-based coating on the diffusion bonding layer area formed after step S4 by coating, spraying or electroplating.

2. The method of joining a Bi-In-Sn liquid metal coating to a titanium alloy substrate according to claim 1, characterized in that, The holding time in step S3 is 6 hours.

3. The method of joining a Bi-In-Sn liquid metal coating to a titanium alloy substrate according to claim 1, wherein The inert gas in step S3 is argon.

4. The method of joining a Bi-In-Sn liquid metal coating to a titanium alloy substrate according to claim 1, wherein The composition of the Bi-based coating in step S5 is the same as or different from that of the low-melting-point Bi-In-Sn alloy in step S2.

5. The method of joining a Bi-In-Sn liquid metal coating to a titanium alloy substrate according to claim 1, wherein The diffusion bonding layer formed in step S3 has a dense and continuous structure, and there are no cracks and pores in the diffusion bonding layer, and the Ti element, Bi element, In element and Sn element in the diffusion bonding layer interdiffuse.

6. The method of joining a Bi-In-Sn liquid metal coating to a titanium alloy substrate according to claim 1, wherein The substrate pretreatment in step 1) further comprises: after mechanical polishing, the surface to be connected is cleaned to remove the residual debris of polishing.

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