A method for wire surface vapor deposition-thermal diffusion composite plating

Abstract

This invention relates to the field of surface treatment technology for metal materials. The invention discloses a vapor deposition-thermal diffusion composite coating method for metal wire surfaces. First, the metal wire substrate undergoes surface pretreatment to obtain a clean surface. Then, a gradient underlayer is prepared using vapor deposition. Next, a high-melting-point metal functional layer is deposited using the same process. Subsequently, the wire is placed in a vacuum or protective atmosphere for low-temperature thermal diffusion treatment, with the temperature below the eutectic and melting phase transition temperatures of the substrate and functional layer. A metallurgical bonding transition layer is formed through atomic diffusion. Finally, post-treatment yields the composite metal wire. This invention's vapor deposition-thermal diffusion composite coating method for metal wires constructs a complete collaborative process system. The gradient underlayer combined with low-temperature thermal diffusion forms a metallurgical bond, solving the pain points of traditional coating processes such as low coating adhesion and high interfacial stress. It also avoids high-temperature damage to the substrate, and the process is universal and can be industrially produced using conventional equipment.

Description

Technical Field

[0001] This invention relates to the field of metal material surface treatment technology, and in particular to a vapor deposition-thermal diffusion composite coating method for metal wire surface. Background Technology

[0002] Metal wires are fundamental components in aerospace, precision machinery, electronic devices, metallurgy, and chemical industries, and their surface properties directly determine the overall efficiency and lifespan of these devices. As industries increasingly demand higher performance from components, it is necessary to coat metal wires with high-melting-point metal functional layers to impart superior properties such as high-temperature resistance, wear resistance, and corrosion resistance. Therefore, the coating process for metal wire surfaces has become crucial for industry research and application. Currently, the industry primarily uses traditional electroplating, single physical vapor deposition, and simple thermal diffusion treatment for surface coating of metal wires. While these methods can achieve basic coating deposition, they struggle to simultaneously address the bonding strength between the coating and the substrate, the mechanical properties of the metal wire substrate, and the overall performance of the coating, making them unsuitable for the stringent application requirements of high-end manufacturing.

[0003] Traditional electroplating is a common method for surface treatment of metal wires. This process achieves coating deposition through electrochemical action, but it has many inherent defects. The coating and the metal wire substrate are only physically attached, with extremely low interfacial adhesion. Under conditions such as repeated bending and high-temperature operation, the coating is prone to peeling and flaking. Furthermore, the coating thickness uniformity of electroplating is poor. Electroplating has poor compatibility with the deposition of high-melting-point metals such as tungsten, molybdenum, and titanium, making it difficult to prepare dense and uniform high-melting-point metal functional layers, which cannot meet the surface performance requirements of high-end applications for metal wires.

[0004] While single physical vapor deposition (PVD) can achieve the deposition of high-melting-point metal functional layers and improve coating density, the lack of a transition underlayer leads to lattice mismatch and significant differences in thermal expansion coefficients between the metal wire substrate and the high-melting-point functional layer. This results in significant interfacial stress and high internal stress within the coating, causing a decrease in the repeated bending performance of the metal wire and making it prone to microcracks. Existing thermal diffusion processes often employ high-temperature treatments without precise temperature control, easily causing coarse grains and deformation in the metal wire substrate, severely damaging the substrate's mechanical properties. Furthermore, current processes lack specific coating solutions designed for the structural characteristics of continuous, slender metal wires, making it difficult to achieve a gradient transition and uniform deposition of coating components. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention discloses a vapor deposition-thermal diffusion composite coating method for metal wire surfaces that is adapted to continuous slender metal wires and takes into account both coating adhesion and substrate performance.

[0006] This invention discloses a vapor deposition-thermal diffusion composite coating method for metal wire surfaces, which includes the following steps:

[0007] Step 1: Perform surface pretreatment on the metal wire substrate to remove oil and oxide layers from its surface and obtain a clean surface;

[0008] Step 2: Using vapor deposition, a base layer with a gradient composition is prepared on the surface of the pretreated metal wire substrate. The parameters of the vapor deposition process change in a gradient during the deposition process to control the composition distribution, microstructure and interfacial bonding state of the base layer with the metal wire substrate.

[0009] Step 3: On the surface of the base layer, continue to deposit a high-melting-point metal functional layer using vapor deposition process;

[0010] Step 4: Place the metal wire with the deposited underlayer and high melting point metal functional layer in a vacuum or protective atmosphere environment and perform low temperature thermal diffusion treatment. The temperature of the low temperature thermal diffusion treatment is lower than the temperature at which the high melting point metal functional layer and the metal wire substrate form a eutectic phase or undergo a melting phase transformation. A metallurgical bonding transition layer is formed at the interface through atomic diffusion.

[0011] Step 5: Perform post-processing on the heat-diffusion treated metal wire to obtain composite metal wire.

[0012] Furthermore, the vapor deposition process in step two is magnetron sputtering, multi-arc ion plating, or electron beam evaporation.

[0013] The deposition rate gradient ranged from 0.1 nm / min to 50 nm / min, and the deposition vacuum gradient ranged from 1.0 × 10⁻⁶. -1 Pa to 1.0 × 10 -3 Pa;

[0014] The gradient change can be either a continuous linear change or a step-like piecewise change.

[0015] Furthermore, in step two, the base material is selected from one or more elemental metals selected from nickel, cobalt, palladium, copper, and chromium, or from one or more alloy materials selected from nickel-chromium alloy, nickel-cobalt alloy, and nickel-copper alloy.

[0016] The total thickness of the base layer is 0.1μm to 5μm.

[0017] Furthermore, in step three, the high-melting-point metal functional layer material is selected from one pure metal or its alloy from titanium, tungsten, molybdenum, niobium, and zirconium.

[0018] The thickness of the high-melting-point metal functional layer ranges from 1 μm to 50 μm, and the thickness uniformity is controlled within ±5% of the average thickness.

[0019] Furthermore, in step four, the temperature of the low-temperature thermal diffusion treatment is 400°C to 900°C, and the holding time is 30 min to 300 min;

[0020] When the metal wire substrate is titanium or titanium alloy and the functional layer is tungsten or molybdenum, the thermal diffusion temperature is preferably 500°C to 700°C.

[0021] When the metal wire substrate is tungsten or molybdenum and the functional layer is titanium or zirconium, the thermal diffusion temperature is preferably 600°C to 800°C.

[0022] Furthermore, in step four, the heating rate of the low-temperature thermal diffusion treatment is 2°C / min to 15°C / min, and the cooling rate is 1°C / min to 10°C / min;

[0023] The heating process adopts a segmented control method, first holding at 200°C to 300°C for 10 to 30 minutes, and then heating up to the target diffusion temperature.

[0024] Furthermore, the vacuum level of the vacuum environment in step four is less than or equal to 1.0 × 10⁻⁶. -2 Pa;

[0025] The protective atmosphere is argon, helium or nitrogen with a purity of not less than 99.99%, and the furnace pressure is controlled at 0.1 atm to 0.8 atm.

[0026] Furthermore, the surface pretreatment in step one includes electrolytic degreasing, acid pickling activation, ultrasonic cleaning, and glow discharge cleaning;

[0027] The current density for electrolytic degreasing is 2 A / dm. 2 Up to 10A / dm 2 The processing time is 30 to 180 seconds;

[0028] The glow discharge cleaning voltage is 500V to 1000V, and the processing time is 5min to 20min.

[0029] After pretreatment, the surface cleanliness of the metal wire substrate reaches over 95%.

[0030] Furthermore, the post-processing in step five includes surface brightening, sizing drawing, and stress-relief annealing;

[0031] Surface brightening treatment is achieved through chemical polishing or electrochemical polishing;

[0032] The stress-relief annealing temperature is 200°C to 400°C, and the holding time is 30 min to 120 min;

[0033] The total deformation during sizing drawing is 10% to 30%.

[0034] Furthermore, the metal wire substrate is a continuous slender wire made of one of the following: steel, stainless steel, copper and copper alloys, nickel and nickel alloys, titanium and titanium alloys, tungsten and tungsten alloys, molybdenum and molybdenum alloys, with an original diameter of 0.01 mm to 5 mm and a length-to-diameter ratio greater than 1000:1.

[0035] The beneficial effects of this invention are:

[0036] This invention presents a composite coating method for metal wire surfaces using vapor deposition and thermal diffusion. It establishes a comprehensive, collaborative process system from surface pretreatment to post-treatment, effectively addressing the pain points of traditional metal wire coating processes, such as low adhesion between the coating and the substrate, high interfacial stress, and poor high-temperature stability. Through gradient underlayer preparation, a continuous transition of composition between the substrate and the high-melting-point metal functional layer is achieved, alleviating interfacial stress caused by lattice mismatch and differences in thermal expansion coefficients. Combined with a metallurgical bonding transition layer formed by low-temperature thermal diffusion, this method changes the traditional process where the coating is merely physically attached. Furthermore, the low-temperature thermal diffusion temperature avoids the eutectic and melting phase transition temperatures of the substrate and functional layer, effectively preventing high-temperature-induced substrate grain coarsening and deformation. This minimizes substrate performance loss while maintaining sufficient adhesion. This process is adaptable to various combinations of metal wire substrates and high-melting-point functional layers. Parameters at each stage are adjustable, and the entire process can be continuously processed using conventional industrial equipment without special customization, demonstrating both process versatility and industrial production feasibility.

[0037] The composite metal wire prepared by this invention achieves comprehensive improvements in various properties, offering advantages over traditional electroplating, single PVD deposition, and high-temperature thermal diffusion processes. The critical load for interfacial bonding is increased, and the coating thickness uniformity is controlled within ±3.5%, meeting high-precision processing requirements. The wire withstands over 100 repeated bending cycles, effectively eliminating internal stress and exhibiting excellent flexibility and structural stability. After holding at 600℃, the bonding strength retention rate reaches over 93%, demonstrating excellent high-temperature performance. The surface roughness Ra value is controlled within 0.13μm, resulting in high surface smoothness suitable for precision device processing. Simultaneously, the post-processing steps achieve dimensional accuracy calibration and surface quality optimization of the metal wire, giving the composite metal wire excellent high-temperature resistance, wear resistance, and reliable mechanical properties. This meets the application needs of multiple fields such as aerospace, precision machinery, and electronic devices, possessing high industrialization value and promising market application prospects. Attached Figure Description

[0038] Figure 1 This is a flowchart of a vapor deposition-thermal diffusion composite coating method for metal wire surface in the embodiments of this application.

[0039] Figure 2 This is a flowchart of a gradient underlayer deposition process in an embodiment of this application.

[0040] Figure 3 This is a flowchart of a low-temperature thermal diffusion process in an embodiment of this application. Detailed Implementation

[0041] To enable those skilled in the art to better understand the present invention, the technical solutions in the specific embodiments of the present invention will be clearly and completely described below.

[0042] This invention discloses a vapor deposition-thermal diffusion composite coating method for metal wire surfaces, which includes the following steps:

[0043] Step 1: Perform surface pretreatment on the metal wire substrate to remove oil and oxide layers from its surface and obtain a clean surface;

[0044] Step 2: Using vapor deposition, a base layer with a gradient composition is prepared on the surface of the pretreated metal wire substrate. The parameters of the vapor deposition process change in a gradient during the deposition process to control the composition distribution, microstructure and interfacial bonding state of the base layer with the metal wire substrate.

[0045] Step 3: On the surface of the base layer, continue to deposit a high-melting-point metal functional layer using vapor deposition process;

[0046] Step 4: Place the metal wire with the deposited underlayer and high melting point metal functional layer in a vacuum or protective atmosphere environment and perform low temperature thermal diffusion treatment. The temperature of the low temperature thermal diffusion treatment is lower than the temperature at which the high melting point metal functional layer and the metal wire substrate form a eutectic phase or undergo a melting phase transformation. A metallurgical bonding transition layer is formed at the interface through atomic diffusion.

[0047] Step 5: Perform post-processing on the heat-diffusion treated metal wire to obtain composite metal wire.

[0048] The metal wire surface vapor deposition-thermal diffusion composite coating method of this invention achieves a strong bond between the coating and the substrate by combining stepwise deposition and low-temperature diffusion. First, the metal wire substrate undergoes a multi-step surface pretreatment process to thoroughly remove adhering oil and oxide layers, creating a clean and stable substrate for subsequent coating deposition. Then, a vapor deposition process is used to sequentially deposit a gradient underlayer and a high-melting-point metal functional layer. Finally, the coated metal wire is placed in a vacuum or protective atmosphere environment for low-temperature thermal diffusion treatment. The treatment temperature is controlled to avoid the temperature range where the high-melting-point metal functional layer and the substrate form a eutectic phase or melt phase transition. A metallurgical bonding transition layer is formed at the interface through atomic diffusion. After coating, post-treatment is used to optimize the overall performance of the metal wire, ultimately obtaining a composite metal wire. This process changes the traditional coating process where the coating and substrate are only physically attached. Metallurgical bonding enhances the bonding strength between the coating and the substrate. Simultaneously, the low-temperature thermal diffusion design effectively avoids problems such as grain coarsening and deformation caused by high-temperature treatment on the metal wire substrate, fully preserving the mechanical properties of the substrate itself.

[0049] This invention achieves the preparation of a gradient underlayer by gradient control of vapor deposition process parameters. During the underlayer deposition process, by changing the vapor deposition process parameters, the composition of the underlayer continuously transitions from the metal wire substrate side to the high-melting-point metal functional layer side. This controls the composition distribution and microstructure of the underlayer, optimizing its interfacial bonding with the metal wire substrate. After the underlayer is prepared, the high-melting-point metal functional layer is directly deposited on its surface using vapor deposition. The entire process does not require changing the processing environment, reducing the possibility of secondary contamination on the metal wire surface. The gradient underlayer design effectively alleviates the interfacial stress caused by lattice mismatch and differences in thermal expansion coefficients between the metal wire substrate and the high-melting-point metal functional layer, improving interfacial compatibility and bonding stability. The continuous vapor deposition process ensures the accuracy of the coating deposition and effectively controls the thickness uniformity of the high-melting-point metal functional layer, resulting in a more stable coating structure.

[0050] This invention improves the overall performance of composite metal wires by constructing a complete process system from surface pretreatment to post-treatment. Each process step is interconnected and works synergistically. The clean substrate from surface pretreatment lays a solid foundation for coating deposition. The deposition of a high-melting-point metal functional layer endows the metal wire with excellent functional properties such as high-temperature resistance and wear resistance. The metallurgical bonding transition layer formed by low-temperature thermal diffusion strengthens the bonding effect between the coating and the substrate. Subsequent post-treatment optimizes the surface quality and dimensional accuracy of the composite metal wire and eliminates internal stress generated during processing. This process method is adapted to the processing characteristics of continuous, slender metal wires. Process parameters can be flexibly adjusted for different metal wire substrates and high-melting-point metal functional layers. Each step of the process has good controllability and operability, enabling continuous industrial production. The resulting composite metal wire not only possesses excellent interfacial bonding and high-temperature stability but also good repeated bending performance, meeting the needs of various application scenarios.

[0051] In one implementation method, the vapor deposition process in step two is magnetron sputtering, multi-arc ion plating, or electron beam evaporation.

[0052] The deposition rate gradient ranged from 0.1 nm / min to 50 nm / min, and the deposition vacuum gradient ranged from 1.0 × 10⁻⁶. -1 Pa to 1.0 × 10 -3 Pa;

[0053] The gradient change can be either a continuous linear change or a step-like piecewise change.

[0054] In this embodiment, the gradient underlayer deposition in step two is completed using a vapor phase deposition process such as magnetron sputtering, multi-arc ion plating, or electron beam evaporation. All three processes are suitable for the coating requirements of slender metal wire structures and can be directly deposited on the pretreated metal wire substrate surface. During the deposition process, by adjusting the power, gas flow rate, and target bias of the equipment, the deposition rate and deposition vacuum degree are allowed to vary gradually within set ranges. Specifically, the deposition rate is adjusted from 0.1 nm / min to 50 nm / min, and the deposition vacuum degree is adjusted within 1.0 × 10⁻⁶ nm / min. -1 Pa to 1.0 × 10 -3 Pa, by adjusting equipment parameters, achieves an orderly gradient change in process parameters during the underlayer deposition process, thereby guiding the metal atoms in the underlayer to deposit according to a preset pattern. All three types of vapor deposition processes have the characteristics of high deposition accuracy and good coating density, which can ensure the initial adhesion between the underlayer and the metal wire substrate from the source and avoid defects such as looseness and pinholes in the coating.

[0055] The gradient range of deposition rate and deposition vacuum degree has been verified and optimized. Within this range, parameter gradient adjustments can be achieved through automated control of the vapor deposition equipment's intelligent control system, eliminating the need for frequent manual intervention and ensuring the stability and consistency of the deposition process. This rate range avoids the low production efficiency caused by excessively slow deposition rates, while also preventing issues such as disordered atomic arrangement and decreased density in the coating caused by excessively fast rates. The gradient range of vacuum degree ensures a consistently high cleanliness of the deposition environment, reducing the incorporation of airborne impurities into the coating. Furthermore, the gradient variation of parameters within this reasonable range allows the composition of the underlayer to gradually transition from the metal wire substrate side to the subsequent functional layer side, achieving a gradient distribution of components and effectively alleviating interfacial stress between the substrate and the underlayer.

[0056] This implementation method allows for flexible selection of either continuous linear or stepped segmented changes in process parameters to achieve gradient adjustment, based on the material matching requirements of the metal wire substrate and the high-melting-point metal functional layer. Both methods can be implemented by pre-setting parameter change curves and nodes through the program control system of the vapor deposition equipment, which will automatically complete the gradient parameter changes according to the preset program. Continuous linear changes allow the deposition rate and vacuum level to change smoothly and gradually throughout the deposition process, achieving a seamless transition of the underlayer composition and a smoother interface. Stepped segmented changes divide the deposition process into multiple stages, maintaining parameter stability within each stage and gradually adjusting parameters between stages, facilitating process control and parameter monitoring. Both gradient change methods can be specifically adapted to the plating requirements of metal wires of different materials and specifications, effectively controlling the composition distribution and microstructure of the underlayer, optimizing the interface bonding between the underlayer and the metal wire substrate, and building a solid transition substrate for the subsequent deposition of the high-melting-point metal functional layer.

[0057] In one implementation, the base material in step two is selected from one or more elemental metals selected from nickel, cobalt, palladium, copper, and chromium, or from one or more alloy materials selected from nickel-chromium alloy, nickel-cobalt alloy, and nickel-copper alloy.

[0058] The total thickness of the base layer is 0.1μm to 5μm.

[0059] In one implementation method, the underlayer material in step two is selected from elemental nickel, cobalt, palladium, copper, or chromium, or nickel-chromium, nickel-cobalt, or nickel-copper alloys. These materials are all suitable for the process characteristics of vapor deposition and can be made into corresponding metal or alloy targets for use in magnetron sputtering, multi-arc ion plating, or electron beam evaporation processes. Depending on the material matching requirements between the metal wire substrate and the subsequent high-melting-point metal functional layer, one element or alloy can be selected as the underlayer material alone, or multiple elements and alloys can be combined. During vapor deposition, relying on the gradient changes in process parameters, an orderly transition of the underlayer material composition between the substrate and the functional layer is achieved, resulting in a good physicochemical property connection between the underlayer and the substrate, and between the underlayer and the functional layer.

[0060] This embodiment controls the total thickness of the underlayer within the range of 0.1 μm to 5 μm. This thickness is achieved through the control of the vapor deposition process. By setting the corresponding deposition rate and time, and combining this with the gradient variation of process parameters, a gradient underlayer of a preset thickness can be deposited on the surface of the metal wire substrate. For metal wire substrates of different diameters and materials, and for different high-melting-point metal functional layer combinations, the specific thickness of the underlayer can be flexibly adjusted within this range to adapt to the plating requirements of various specifications of metal wires, such as fine and thick diameters, and to meet the interface transition requirements in different application scenarios.

[0061] In one implementation method, the high-melting-point metal functional layer material in step three is selected from one pure metal or an alloy of titanium, tungsten, molybdenum, niobium, and zirconium.

[0062] The thickness of the high-melting-point metal functional layer ranges from 1 μm to 50 μm, and the thickness uniformity is controlled within ±5% of the average thickness.

[0063] As one implementation method, the high-melting-point metal functional layer in step three uses pure metals or alloys of titanium, tungsten, molybdenum, niobium, and zirconium. These materials all have excellent high-melting-point characteristics and are well-suited to vapor deposition processes. Depending on the actual application requirements of the composite metal wire, one pure metal or alloy can be selected as the functional layer material. After it is made into the corresponding coating target, vapor deposition is carried out directly on the surface of the metal wire after the underlayer deposition is completed. There is no need to change the processing environment throughout the process. Relying on the atomic-level deposition characteristics of vapor deposition, the high-melting-point metal functional layer and the underlayer are tightly connected, ensuring the continuity of the coating structure.

[0064] This embodiment controls the thickness of the high-melting-point metal functional layer within the range of 1μm to 50μm. This thickness can be achieved by adjusting the vapor deposition rate and deposition time. The specific thickness of the functional layer can be flexibly adjusted within this range based on the specifications of the metal wire substrate, the characteristics of the underlayer, and the functional requirements of the composite metal wire. Simultaneously, the thickness uniformity of the functional layer is controlled within ±5% of the average thickness. Utilizing the temperature and pressure control characteristics of the vapor deposition process, combined with continuous and uniform feeding of the metal wire into the tooling, the deposition rate and deposition amount at various locations on the metal wire surface remain consistent. By strictly controlling the fluctuation range of process parameters, a uniform distribution of the functional layer thickness is achieved.

[0065] The material, thickness, and uniformity design of the high-melting-point metal functional layer endow the composite metal wire with excellent and stable functional properties. The selected high-melting-point pure metals and alloys enable the composite metal wire to possess excellent properties such as high temperature resistance, wear resistance, and corrosion resistance, making it suitable for various demanding applications such as aerospace, precision machinery, and electronic devices. Thickness uniformity within ±5% ensures consistent functional performance across the surface of the composite metal wire, eliminating localized weak points and improving the overall structural stability and reliability. It also lays a uniform structural foundation for subsequent low-temperature thermal diffusion treatment, ensuring uniform atomic diffusion at the interface.

[0066] In one implementation method, the temperature of the low-temperature thermal diffusion treatment in step four is 400°C to 900°C, and the holding time is 30 min to 300 min;

[0067] When the metal wire substrate is titanium or titanium alloy and the functional layer is tungsten or molybdenum, the thermal diffusion temperature is preferably 500°C to 700°C.

[0068] When the metal wire substrate is tungsten or molybdenum and the functional layer is titanium or zirconium, the thermal diffusion temperature is preferably 600°C to 800°C.

[0069] In one implementation method, the low-temperature thermal diffusion treatment in step four requires placing the metal wire with the deposited underlayer and high-melting-point metal functional layer inside a dedicated diffusion furnace under vacuum or protective atmosphere. The furnace's temperature control system sets and executes the thermal diffusion process, stabilizing the overall thermal diffusion temperature between 400°C and 900°C. The holding time is flexibly adjusted within the range of 30 to 300 minutes, depending on the material combination of the metal wire substrate and the high-melting-point metal functional layer, the coating thickness, and other practical factors. The diffusion furnace's temperature control system can monitor the furnace temperature in real time and perform dynamic compensation, ensuring no temperature fluctuations throughout the entire thermal diffusion process. This provides a stable temperature environment for the orderly diffusion of metal atoms, guaranteeing the formation effect of the metallurgical bonding transition layer at the interface.

[0070] This embodiment establishes targeted preferred thermal diffusion temperature ranges based on the different material matching characteristics of the metal wire substrate and the high-melting-point metal functional layer. These preferred ranges are achieved by adjusting the heating program and temperature control parameters of the diffusion furnace. When the metal wire substrate is titanium or a titanium alloy and the functional layer is tungsten or molybdenum, the target temperature of the diffusion furnace is adjusted to a preferred range of 500°C to 700°C; when the metal wire substrate is tungsten or molybdenum and the functional layer is titanium or zirconium, the target temperature is adjusted to a preferred range of 600°C to 800°C. The setting of different preferred ranges is based on the atomic diffusion rate, lattice matching degree, and thermal expansion characteristics of various metals, and the atomic diffusion process is adapted to the material properties through temperature control.

[0071] The temperature and holding time range design, along with the targeted optimal temperature settings, offers advantages in both process and performance. The overall temperature range of 400°C to 900°C remains consistently below the temperature at which the high-melting-point metal functional layer and the metal wire substrate form a eutectic phase or undergo a molten phase transformation. This effectively avoids grain coarsening and deformation of the metal wire substrate caused by high temperatures, as well as defects in the fusion bonding between the coating and the substrate, thus fully preserving the mechanical properties of the substrate itself. The holding time of 30 to 300 minutes ensures sufficient time for metal atoms to diffuse at the interface, forming a continuous and dense metallurgical bonding transition layer, while preventing reduced production efficiency or deterioration of coating performance due to excessively long holding times. Furthermore, the optimized temperature ranges set for different material combinations closely align with the atomic diffusion patterns of the corresponding metals, allowing for more complete and uniform atomic diffusion at the interface. This results in a more stable metallurgical bonding transition layer structure, enhancing the interfacial bonding strength of the composite metal wire. Simultaneously, this process can adapt to various combinations of substrates and functional layers, improving its versatility and adaptability.

[0072] In one implementation, the heating rate of the low-temperature thermal diffusion treatment in step four is 2°C / min to 15°C / min, and the cooling rate is 1°C / min to 10°C / min;

[0073] The heating process adopts a segmented control method, first holding at 200°C to 300°C for 10 to 30 minutes, and then heating up to the target diffusion temperature.

[0074] In one implementation method, the low-temperature thermal diffusion treatment in step four utilizes the intelligent temperature control system of a dedicated diffusion furnace to regulate the heating and cooling rates and control the heating process in segments. Based on the material combination of the metal wire substrate and the high-melting-point metal functional layer, as well as the coating thickness, the heating rate is flexibly set within the range of 2°C / min to 15°C / min, while the cooling rate is adjusted within the range of 1°C / min to 10°C / min. During the heating phase, segmented control is executed according to a preset program. First, the furnace temperature is raised to the range of 200°C to 300°C and maintained for 10 to 30 minutes. After this holding period, the temperature control system continues to raise the temperature to the target diffusion temperature at the set heating rate. Throughout the process, data is collected in real-time and dynamically compensated through the furnace's temperature monitoring module to ensure a stable heating and cooling rate without fluctuations and controllable holding time.

[0075] This embodiment limits the heating and cooling rate range based on the diffusion law of metal atoms and the structural characteristics of the composite metal wire. This rate range is controlled by adjusting the power of the heating and cooling modules of the diffusion furnace. Controlling the heating rate within this range allows the temperature of the metal wire substrate and the coating to gradually increase, providing stable diffusion momentum for atoms at the interface, achieving orderly diffusion, and avoiding localized thermal stress caused by excessively rapid heating, thus preventing micro-cracks in the coating or peeling from the substrate. A reasonable cooling rate allows the composite metal wire to cool slowly from a high temperature, reducing uneven thermal shrinkage caused by sudden cooling, preventing cracking and peeling of the coating due to internal stress concentration, and ensuring the structural stability of the metallurgical bonding transition layer, allowing atoms to complete orderly arrangement during cooling.

[0076] The segmented temperature control during the heating process lays a stable technological foundation for low-temperature thermal diffusion treatment. Short-term temperature holding within the range of 200°C to 300°C can gradually eliminate the deposition stress generated by the metal wire during the vapor deposition of the underlayer and functional layer. This prevents the concentrated release of this stress during the subsequent diffusion stage at higher temperatures, which could lead to coating deformation or interfacial bonding defects. Simultaneously, this temperature holding stage ensures a uniform temperature across the entire metal wire, eliminating uneven heating caused by localized temperature differences. This ensures that the atomic diffusion rate remains consistent across all locations on the metal wire surface after reaching the target diffusion temperature, resulting in a denser and more uniform metallurgical bonding transition layer at the interface. This enhances the interfacial bonding strength of the composite metal wire and guarantees the overall structural integrity and performance stability of the coating.

[0077] In one implementation method, the vacuum level of the vacuum environment in step four is less than or equal to 1.0 × 10⁻⁶. -2 Pa;

[0078] The protective atmosphere is argon, helium or nitrogen with a purity of not less than 99.99%, and the furnace pressure is controlled at 0.1 atm to 0.8 atm.

[0079] As an implementation method, for the low-temperature thermal diffusion treatment in Step 4, it can be flexibly carried out in either a vacuum or a protective atmosphere environment according to the material combination requirements of the wire substrate and the high-melting-point metal functional layer. When choosing a vacuum environment, the furnace cavity is evacuated by means of the high-vacuum pumping system supporting the diffusion furnace, and the vacuum degree inside the furnace is monitored in real time through the vacuum detection module inside the furnace, and it is controlled within the range of less than or equal to 1.0×10-2 Pa, maintaining a stable and non-fluctuating vacuum state throughout the process. When choosing a protective atmosphere environment, first perform a pre-evacuation treatment on the furnace cavity, and then fill the furnace with argon, helium or nitrogen with a purity not lower than 99.99%. Use the pressure control system of the furnace body to adjust and maintain the pressure inside the furnace within the range of 0.1 atm to 0.8 atm, ensuring that the protective atmosphere is evenly distributed inside the furnace cavity, providing a stable atmosphere environment for low-temperature thermal diffusion.

[0080] The vacuum degree is controlled within the range of less than or equal to 1.0×10 -2 Pa, which can effectively remove the residual gases inside the furnace cavity, reduce the content of impurities such as oxygen and water vapor, avoid oxidation reactions of the wire substrate, the underlayer and the high-melting-point metal functional layer during the thermal diffusion process, and prevent impurity particles from mixing into the interface and affecting the atomic diffusion effect. At the same time, the low-vacuum environment can reduce the hindrance of gas molecules to the diffusion of metal atoms, enabling the atoms between the underlayer and the substrate, and between the underlayer and the functional layer to diffuse with each other more smoothly, promoting the formation of a metallurgical bonding transition layer at the interface. Moreover, this vacuum degree range can be stably achieved by industrial conventional vacuum equipment without special customized equipment, taking into account both the process effect and the production operability.

[0081] The parameter design of the protective atmosphere and the furnace pressure provides a more adaptable environment selection for the low-temperature thermal diffusion treatment. High-purity argon, helium and nitrogen are all inert gases, which can effectively isolate external oxygen and avoid oxidation of the coating and the substrate. Different inert gases can be flexibly selected according to the material characteristics of the substrate and the functional layer to adapt to various process combination requirements. The furnace pressure range of 0.1 atm to 0.8 atm has been verified by the process. This pressure can make the protective atmosphere evenly fill the inside of the furnace cavity, ensuring that all positions on the surface of the wire are in the same atmosphere environment, enabling atomic diffusion to proceed evenly on the entire surface of the wire and avoiding problems of uneven local diffusion. At the same time, this pressure range will neither cause the protective atmosphere to be easily lost due to too low pressure nor hinder the diffusion movement of atoms due to too high pressure, making the thermal diffusion process more efficient. The optional design of the two environments of vacuum and protective atmosphere also enables this process to adapt to different production conditions and processing requirements, improving the versatility and adaptability of the process.

[0082] As an implementation method, the surface pretreatment in Step 1 includes electrolytic degreasing, pickling activation, ultrasonic cleaning and glow discharge cleaning;

[0083] The current density of electrolytic degreasing is 2 A / dm2 Up to 10A / dm 2 The processing time is 30 to 180 seconds;

[0084] The glow discharge cleaning voltage is 500V to 1000V, and the processing time is 5min to 20min.

[0085] After pretreatment, the surface cleanliness of the metal wire substrate reaches over 95%.

[0086] In one implementation method, the surface pretreatment in step one is carried out sequentially in the order of electrolytic degreasing, acid pickling and activation, ultrasonic cleaning, and glow discharge cleaning, progressively completing the surface cleaning and activation of the metal wire substrate. During electrolytic degreasing, the metal wire substrate is placed in the degreasing solution, and the current density is controlled at 2A / dm² by adjusting the power supply system. 2 Up to 10A / dm 2 The processing time is flexibly adjusted from 30 to 180 seconds depending on the degree of oil contamination on the substrate surface, achieving complete removal of surface oil. Acid pickling activation involves immersing the substrate in acid to remove the surface oxide layer, followed by thorough rinsing with pure water. Acid pickling activation can use dilute hydrochloric acid, dilute sulfuric acid, etc., with the concentration and processing time adjusted according to the substrate material. The substrate is then placed in ultrasonic cleaning equipment, where ultrasonic vibration removes residual acid and fine impurities from the surface. Finally, glow discharge cleaning is performed. The substrate is placed in specialized equipment, with the voltage adjusted between 500V and 1000V, and a processing time of 5 to 20 minutes set according to the substrate material. This completes deep surface activation and cleaning, achieving a surface cleanliness of over 95% for the metal wire substrate.

[0087] This embodiment sets a reasonable control range for the process parameters of electrolytic degreasing and glow discharge cleaning. This parameter range has been determined through multiple process verifications and can ensure cleaning effect while maintaining the surface integrity of the metal wire substrate. The current density and processing time range for electrolytic degreasing avoids the problem of incomplete oil removal caused by too low parameters or too short time, and also prevents corrosion or over-corrosion of the substrate surface caused by too high parameters or too long time, adapting to the treatment needs of metal wire substrates with different degrees of oil adhesion. The voltage and time range for glow discharge cleaning can achieve sufficient etching of impurities on the substrate surface and effective improvement of surface energy, while avoiding microscopic damage to the surface of the metal wire substrate caused by excessive voltage or excessive processing time, thus preserving the original surface morphology and mechanical properties of the substrate.

[0088] The coordinated operation and parameter control of four pretreatment processes ensure that the metal wire substrate achieves a highly clean and active surface state. A surface cleanliness level exceeding 95% completely eliminates unfavorable factors affecting coating adhesion, such as oil, oxide layers, and impurities, preventing defects like loose coatings, pinholes, and weak adhesion during subsequent undercoat deposition. The surface activation effect of glow discharge cleaning enhances the adhesion of the substrate surface, allowing the metal atoms in the gradient undercoat to achieve a tight initial bond with the substrate surface. Simultaneously, the uniform clean surface ensures uniform coating growth during subsequent vapor deposition, controlling the process quality of composite coating from the source and improving the overall interfacial bonding between the coating and the substrate.

[0089] In one implementation, the post-processing in step five includes surface brightening, sizing drawing, and stress-relief annealing;

[0090] Surface brightening treatment is achieved through chemical polishing or electrochemical polishing;

[0091] The stress-relief annealing temperature is 200°C to 400°C, and the holding time is 30 min to 120 min;

[0092] The total deformation during sizing drawing is 10% to 30%.

[0093] In one implementation method, the post-processing in step five is performed sequentially: surface brightening, sizing and drawing, and stress-relief annealing. This process optimizes the multi-dimensional performance and dimensions of the composite metal wire after low-temperature thermal diffusion treatment. Surface brightening can be flexibly performed using chemical polishing or electrochemical polishing, depending on the characteristics of the substrate and coating materials of the composite metal wire. The corresponding polishing process eliminates surface defects generated during plating and thermal diffusion. After brightening, sizing and drawing are performed using precision wire drawing equipment, controlling the total deformation within the range of 10% to 30% to ensure the diameter accuracy of the metal wire. Finally, stress-relief annealing is performed. The composite metal wire is placed in a dedicated annealing furnace, and the furnace temperature is controlled between 200°C and 400°C. The holding time is set between 30 minutes and 120 minutes based on the internal stress distribution. After completion, the wire is cooled in the furnace, achieving process control throughout the entire post-processing workflow.

[0094] This implementation method sets reasonable ranges for the process parameters of sizing drawing and stress-relief annealing, and each parameter can be controlled using specialized equipment. The total deformation of sizing drawing is achieved by adjusting the specifications of the drawing die and controlling the drawing rate and number of passes. Within this range, the deformation can achieve the calibration of the metal wire diameter without causing coating cracking or a decrease in the mechanical properties of the substrate due to excessive deformation. The temperature and holding time of stress-relief annealing are controlled by the intelligent temperature control system of the annealing furnace, which can be flexibly adjusted according to the specifications and internal stress of the composite metal wire. This temperature range is always lower than the phase transformation temperature between the coating and the substrate, avoiding damage to the metallurgical bonding transition layer caused by high temperature. The holding time ensures that the internal stress is fully released without reducing production efficiency. The flexible selection of chemical polishing and electrochemical polishing can adapt to the surface treatment requirements of different substrates such as titanium alloys, tungsten, stainless steel, and copper, ensuring the effect and applicability of bright treatment.

[0095] The coordinated operation of the three post-processing steps enhances the overall performance of the composite metal wire in terms of surface quality, dimensional accuracy, and internal stress, making the product more suitable for practical applications. Surface brightening effectively removes defects such as oxide spots and deposited burrs from the composite metal wire surface, reducing surface roughness and improving surface smoothness, while also enhancing the corrosion resistance of the coating. Sizing and drawing, while calibrating the wire diameter and ensuring dimensional consistency and accuracy, uses appropriate plastic deformation to achieve a denser bond between the coating and the substrate, improving interfacial adhesion. Stress-relief annealing completely eliminates the internal stress generated during vapor deposition, low-temperature thermal diffusion, and sizing and drawing, preventing coating cracking, peeling, or wire deformation during subsequent use. It also improves the wire's repeated bending performance and structural stability, giving the composite metal wire both excellent functional characteristics and reliable mechanical properties.

[0096] In one embodiment, the metal wire substrate is a continuous slender wire made of one of steel, stainless steel, copper and copper alloys, nickel and nickel alloys, titanium and titanium alloys, tungsten and tungsten alloys, molybdenum and molybdenum alloys, with an original diameter of 0.01 mm to 5 mm and a length-to-diameter ratio greater than 1000:1.

[0097] As one implementation method, the metal wire substrate of this process can be selected from steel, stainless steel, copper and copper alloys, nickel and nickel alloys, titanium and titanium alloys, tungsten and tungsten alloys, molybdenum and molybdenum alloys. All types of substrates are made into continuous slender wires by relying on mature industrial drawing, rolling and drawing forming processes. The original diameter of the substrate can be flexibly set in the range of 0.01mm to 5mm according to the actual application requirements. At the same time, through forming process control, it is ensured that the length to diameter ratio of the wire is greater than 1000:1.

[0098] This embodiment covers a variety of commonly used metals and alloys for the metal wire substrate. All materials are widely used in industrial production and have mature manufacturing technologies, allowing for targeted selection based on the specific application scenarios and performance requirements of the composite metal wire. Titanium and titanium alloy substrates are lightweight and high-strength; tungsten and molybdenum alloy substrates offer excellent high-temperature resistance; copper and copper alloy substrates have good electrical and thermal conductivity; stainless steel substrates provide good corrosion resistance; nickel and nickel alloy substrates offer strong compatibility; and steel substrates are inexpensive and possess excellent mechanical properties. This diverse range of material choices allows this process to meet the application needs of various fields such as aerospace, electronics, precision machinery, metallurgy, and chemicals. Furthermore, all substrates can achieve good performance synergy with subsequent gradient underlayers and high-melting-point metal functional layers.

[0099] This embodiment features a rationally designed specification parameter for the metal wire substrate. The original diameter range of 0.01mm to 5mm covers various wire specifications, including micro-diameter, fine-diameter, and standard-diameter wires. This caters to the needs of microelectronic components and precision sensors requiring fine-diameter metal wires, while also meeting the requirements of conventional industrial applications for coarse-diameter metal wires, thus offering a wide range of applications. The continuous, slender structure with a length-to-diameter ratio greater than 1000:1 not only matches the continuous and batch production modes in industry, enabling streamlined processing with winding vapor deposition equipment and continuous thermal diffusion furnaces to improve production efficiency, but also ensures uniform heating and stress on the metal wire throughout the entire plating process. This allows for orderly and uniform deposition and atomic diffusion on the wire surface, structurally guaranteeing the quality of composite plating. Furthermore, the metal wire substrates of this specification are all conventional industrial products, with readily available raw materials and low processing difficulty.

[0100] Example

[0101] Example 1

[0102] 1. Substrate: TC4 titanium alloy wire, 0.5mm in diameter, length-to-diameter ratio 5000:1, with no obvious scratches or oxide spots on the substrate surface.

[0103] 2. Instruments: HH-S2 type electrolytic degreasing tank, KQ-500DE type ultrasonic cleaner, PG-1000 type glow discharge cleaning device, JGP-450 type magnetron sputtering coating machine (equipped with tungsten target and nickel-chromium target), ZKL-600 type vacuum diffusion furnace, LD-100 type precision wire drawing machine.

[0104] Step 1: Surface Pretreatment

[0105] (1) Electrolytic degreasing: The TC4 titanium alloy wire is placed in the HH-S2 type electrolytic degreasing tank, and an alkaline degreasing solution (50g / L sodium hydroxide, 30g / L sodium carbonate, 20g / L sodium phosphate, temperature 60℃) is used, with the current density controlled at 6A / dm. 2Processing time: 90 seconds; removes surface oil and dirt.

[0106] (2) Pickling and activation: Soak in 5% hydrochloric acid solution (room temperature) for 15 seconds to remove the surface oxide layer, and then rinse with deionized water 3 times;

[0107] (3) Ultrasonic cleaning: Put the titanium alloy wire into the KQ-500DE ultrasonic cleaner, use deionized water as the cleaning medium, power 200W, clean for 10 minutes to remove residual acid and impurities on the surface.

[0108] (4) Glow discharge cleaning: The cleaned titanium alloy wire is placed into a PG-1000 glow discharge cleaning device, with a controlled voltage of 800V and a vacuum degree of 5.0×10⁻⁶. -2 Pa, processing time 15 min, the final substrate surface cleanliness reached 98%, with no oil stains, oxide layer and impurity residue.

[0109] Step 2: Gradient deposition of the bottom layer

[0110] Process: A JGP-450 magnetron sputtering coating machine was used, and a Ni80Cr20 alloy target was selected as the target material for the underlayer coating.

[0111] Gradient variation of deposition parameters: Vacuum degree from 1.0 × 10 -1 Pa decreased linearly to 5.0 × 10⁻⁶. -3 Pa (gradient change time 30 min), the deposition rate linearly increased from 10 nm / min to 30 nm / min, and the target power linearly increased from 100 W to 300 W;

[0112] The total thickness of the base layer is 1.2 μm. Metallographic microscopy revealed that the composition from the substrate side to the functional layer side showed a gradient increase in Ni and a gradient decrease in Cr, with a uniform transition and no obvious delamination.

[0113] Step 3: Deposition of high-melting-point metal functional layer

[0114] The same JGP-450 magnetron sputtering coating machine was used, but a pure tungsten target was replaced, and a vacuum degree of 5.0 × 10⁻⁶ was maintained. -3 Pa, deposition rate 25 nm / min, target power 400 W, deposited tungsten (W) functional layer with a total thickness of 15 μm, thickness uniformity was ±3.2% as tested according to GB / T6462-2005 standard.

[0115] Step 4: Low-temperature thermal diffusion treatment

[0116] The deposited titanium alloy wire was placed in a ZKL-600 vacuum diffusion furnace and evacuated to a vacuum level of 5.0 × 10⁻⁶. -3Pa; control the heating rate at 8℃ / min, hold at 250℃ for 20min (to eliminate internal stress from deposition), then continue heating to 550℃ and hold for 120min; control the cooling rate at 5℃ / min, and allow to cool naturally to room temperature, forming a uniform metallurgical bonding transition layer at the interface through atomic diffusion.

[0117] Step 5: Post-processing

[0118] (1) Surface brightening treatment: Electrochemical polishing was used, with a phosphoric acid-sulfuric acid mixture (volume ratio 3:1) as the electrolyte, at a temperature of 50℃ and a current density of 8A / dm³. 2 The processing time is 30 seconds, resulting in a bright and flawless surface.

[0119] (2) Sizing and drawing: The LD-100 precision wire drawing machine is used to control the total deformation by 15% to ensure uniform wire diameter;

[0120] (3) Stress-relief annealing: The drawn composite wire is placed in a vacuum annealing furnace at 300℃ and held for 60 minutes. It is then cooled in the furnace to eliminate the internal stress of the drawing and obtain the final composite metal wire.

[0121] Example 2: Pure tungsten wire coated with titanium composite wire

[0122] Substrate: Pure tungsten wire, 0.3mm in diameter, aspect ratio 8000:1

[0123] Instruments: Multi-arc ion plating equipment, atmosphere-protected diffusion furnace, electrochemical polishing machine;

[0124] Step 1: Surface pretreatment electrolytic degreasing: current density 5A / dm 2 Processing time: 60 seconds; ultrasonic cleaning and glow discharge cleaning (voltage 700V, 10 minutes), cleanliness: 97%.

[0125] Step 2: Gradient underlayer deposition process: multi-arc ion plating; underlayer material: pure copper (Cu); deposition parameters changed in a stepwise manner: vacuum degree increased in three stages from 8.0 × 10⁻⁶. -2 Pa decreased to 3.0 × 10 -3 Pa, the deposition rate increased from 5 nm / min to 20 nm / min; the total thickness of the substrate was 0.8 μm.

[0126] Step 3: Deposition of high melting point metal functional layer. Multi-arc ion plating is used to deposit a titanium (Ti) functional layer with a thickness of 10 μm and a thickness uniformity of ±2.8%.

[0127] Step 4: Low-temperature thermal diffusion treatment. Protective atmosphere: 99.995% argon, furnace pressure 0.3 atm; heating rate 10℃ / min, hold at 300℃ for 15min, then heat to 700℃ and hold for 150min; cooling rate 6℃ / min.

[0128] Step 5: Post-treatment chemical polishing; sizing drawing deformation of 12%; stress-relief annealing: 350℃, hold for 90 min.

[0129] Example 3: 304 stainless steel wire with molybdenum coating composite wire

[0130] Base material: 304 stainless steel wire, 1.0mm in diameter, length-to-diameter ratio 3000:1;

[0131] Instruments: Electron beam evaporation equipment, vacuum diffusion furnace, stress-relief annealing furnace

[0132] Step 1: Surface pretreatment electrolytic degreasing: current density 8A / dm 2 Processing time 120s; Glow discharge cleaning (voltage 900V, 18min), cleanliness 99%.

[0133] Step 2: Gradient underlayer deposition process: electron beam evaporation; underlayer material: nickel-cobalt alloy (Ni70Co30); deposition parameters continuously and linearly changed: vacuum degree from 6.0×10 -2 Pa decreased to 4.0 × 10 -3 Pa, the deposition rate increased from 15 nm / min to 40 nm / min; the total thickness of the substrate was 2.0 μm.

[0134] Step 3: Deposition of high melting point metal functional layer. Electron beam evaporation is used to deposit a molybdenum (Mo) functional layer with a thickness of 20 μm and a thickness uniformity of ±3.5%.

[0135] Step 4: Low-temperature thermal diffusion treatment with a vacuum degree of 8.0 × 10⁻⁶ -3 Pa; heating rate 6℃ / min, hold at 280℃ for 25min, then heat to 600℃ and hold for 180min; cooling rate 4℃ / min.

[0136] Step 5: Post-treatment electrochemical polishing; sizing drawing deformation amount 20%; stress relief annealing: 280℃, hold for 80 min.

[0137] Example 4: Pure copper wire plated with tantalum composite wire

[0138] Substrate: Pure copper wire, 0.1mm in diameter, aspect ratio 10000:1;

[0139] Instruments: Magnetron sputtering coating machine, atmosphere diffusion furnace

[0140] Step 1: Surface pretreatment electrolytic degreasing: current density 3A / dm 2 Processing time: 45 seconds; ultrasonic cleaning and glow discharge cleaning (voltage 600V, 8 minutes), cleanliness: 96%.

[0141] Step 2: Gradient underlayer deposition process: magnetron sputtering; underlayer material: pure nickel (Ni); linear change in deposition parameters: vacuum level from 9.0 × 10⁻⁶ -2 Pa decreased to 6.0 × 10 -3 Pa, the deposition rate increased from 8 nm / min to 25 nm / min; the total thickness of the substrate was 0.5 μm.

[0142] Step 3: Deposition of high melting point metal functional layer. A tantalum (Ta) functional layer is deposited by magnetron sputtering with a thickness of 8 μm and a thickness uniformity of ±2.5%.

[0143] Step 4: Low-temperature thermal diffusion treatment with 99.99% nitrogen protection at a pressure of 0.5 atm; heating rate of 5℃ / min, holding at 220℃ for 18 min, then heating to 500℃ and holding for 90 min; cooling rate of 3℃ / min.

[0144] Step 5: Post-treatment chemical polishing; sizing drawing deformation amount 10%; stress relief annealing: 250℃, hold for 50 min.

[0145] Example 5: Pure molybdenum wire coated with zirconium composite wire

[0146] Substrate: Pure molybdenum wire, 0.8mm in diameter, aspect ratio 4000:1;

[0147] Instruments: Multi-arc ion plating equipment, vacuum diffusion furnace

[0148] Step 1: Surface pretreatment electrolytic degreasing: current density 7A / dm 2 Processing time 80s; Glow discharge cleaning (voltage 850V, 12min), cleanliness 98%.

[0149] Step 2: Gradient underlayer deposition process: multi-arc ion plating; underlayer material: pure chromium (Cr); deposition parameters changed stepwise: vacuum degree from 7.0 × 10⁻⁶ -2 Pa decreased to 5.0 × 10 -3 Pa, the deposition rate increased from 12 nm / min to 35 nm / min; the total thickness of the substrate was 1.5 μm.

[0150] Step 3: Deposition of high melting point metal functional layer. Multi-arc ion plating deposits a zirconium (Zr) functional layer with a thickness of 12 μm and a thickness uniformity of ±3.0%.

[0151] Step 4: Low-temperature thermal diffusion treatment with a vacuum degree of 6.0 × 10⁻⁶ -3 Pa; heating rate 12℃ / min, hold at 260℃ for 22min, then heat to 750℃ and hold for 200min; cooling rate 7℃ / min.

[0152] Step 5: Post-treatment electrochemical polishing; sizing drawing deformation amount 18%; stress relief annealing: 320℃, hold for 70 min.

[0153] Comparative Example

[0154] Comparative Example 1: Traditional electroplated tungsten layer (no vapor deposition, no gradient underlayer, no thermal diffusion)

[0155] Substrate: TC4 titanium alloy wire, same as in Example 1, with a diameter of 0.5 mm;

[0156] Process: After conventional degreasing, a tungsten layer is directly electroplated with a thickness of 15μm. There is no undercoat, no thermal diffusion, and no post-treatment drawing.

[0157] It is merely a physical adhesion, without any metallurgical bonding.

[0158] Comparative Example 2: Single PVD Deposited Tungsten Layer

[0159] Substrate: TC4 titanium alloy wire, same as in Example 1, with a diameter of 0.5 mm;

[0160] Process: After conventional cleaning, a 15μm tungsten layer is directly deposited by magnetron sputtering, without gradient layering and without thermal diffusion treatment.

[0161] The interface is physically bonded, with high internal stress and no diffusion transition layer.

[0162] Comparative Example 3: High-Temperature Thermal Diffusion Tungsten Plating

[0163] Substrate: TC4 titanium alloy wire, same as in Example 1, with a diameter of 0.5 mm;

[0164] Process: No gradient underlayer deposition, followed by direct deposition of tungsten layer, high-temperature thermal diffusion at 1100℃, and holding at that temperature for 60 minutes.

[0165] High-temperature deformation of the substrate and coarse grains lead to a decrease in the mechanical properties of the filament.

[0166] Performance testing methods

[0167] Interfacial adhesion test: According to GB / T31984-2015 "Micro-scratch test method for determining the interfacial adhesion of thin films", a nano-scratch tester was used with a loading rate of 50 N / min. The critical load for coating peeling was recorded. The greater the load, the stronger the adhesion.

[0168] Coating thickness and uniformity test: According to GB / T6462-2005 "Measuring the thickness of cross sections of metals and alloys under corrosion", cross sections were measured using a metallographic microscope, and the thickness deviation at multiple points was calculated. Uniformity = (maximum thickness - minimum thickness) / average thickness × 100%.

[0169] Repeated bending performance test: According to GB / T238-2013 "Metallic materials wire repeated bending test method", the bending radius of wire with diameter ≤1mm is 1mm, and the number of bending without breaking is recorded.

[0170] High temperature stability test: The sample was placed in an argon atmosphere at 600℃ for 2 hours. After cooling, the coating was observed to see if it peeled or fell off, and the adhesion retention rate was tested.

[0171] Surface roughness test: The Ra value was tested using a surface profilometer in accordance with GB / T1031-2009 "Product Geometric Specification (GPS) Surface Structure Profilometry".

[0172] The performance test data comparison is shown in Table 1 below.

[0173] Table 1

[0174] The performance test data clearly show that the composite metal wire prepared by this invention outperforms samples prepared by traditional electroplating, single PVD deposition, and high-temperature thermal diffusion processes in all aspects. The critical load for interfacial bonding in each embodiment is above 38.5 N, more than four times that of traditional electroplating, and far exceeds that of single PVD deposition and high-temperature thermal diffusion processes. The metallurgical bond formed by gradient undercoating and low-temperature thermal diffusion solves the problem of only physical adhesion between the coating and the substrate in traditional processes. The coating thickness uniformity is controlled within ±3.5%, far superior to the ±8.6% of the comparative example. Precise parameter control of vapor phase deposition ensures the uniformity of the coating. The number of repeated bending cycles in each embodiment exceeds 100, a significant improvement compared to the highest 48 cycles in the comparative example. The complete elimination of internal stress gives the composite metal wire excellent toughness. After holding at 600℃, the bonding strength retention rate is above 93%, demonstrating outstanding high-temperature stability. The surface roughness Ra value is within 0.13 μm, indicating excellent surface quality. This process, through collaborative design across the entire process, from gradient undercoating to low-temperature thermal diffusion treatment, achieves complementary and synergistic effects across multiple stages, solving many pain points of traditional plating processes, improving the overall performance of composite metal wires, adapting to various industrial application scenarios, and possessing significant industrialization value.

[0175] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for vapor deposition-thermal diffusion composite coating of metal wire surface, characterized in that, Includes the following steps: Step 1: Perform surface pretreatment on the metal wire substrate to remove oil and oxide layers from its surface and obtain a clean surface; Step 2: Using vapor deposition, a base layer with a gradient composition is prepared on the surface of the pretreated metal wire substrate. The parameters of the vapor deposition process change in a gradient during the deposition process to control the composition distribution, microstructure and interfacial bonding state of the base layer with the metal wire substrate. Step 3: On the surface of the base layer, continue to deposit a high-melting-point metal functional layer using vapor deposition process; Step 4: Place the metal wire with the deposited underlayer and high melting point metal functional layer in a vacuum or protective atmosphere environment and perform low temperature thermal diffusion treatment. The temperature of the low temperature thermal diffusion treatment is lower than the temperature at which the high melting point metal functional layer and the metal wire substrate form a eutectic phase or undergo a melting phase transformation. A metallurgical bonding transition layer is formed at the interface through atomic diffusion. Step 5: Perform post-processing on the heat-diffusion treated metal wire to obtain composite metal wire.

2. The method for vapor deposition-thermal diffusion composite coating of metal wire surface according to claim 1, characterized in that: In step two, the vapor deposition process is magnetron sputtering, multi-arc ion plating, or electron beam evaporation. The deposition rate gradient ranged from 0.1 nm / min to 50 nm / min, and the deposition vacuum gradient ranged from 1.0 × 10⁻⁶. -1 Pa to 1.0 × 10 -3 Pa; The gradient change can be either a continuous linear change or a step-like piecewise change.

3. The method for vapor deposition-thermal diffusion composite coating of metal wire surface according to claim 1, characterized in that: In step two, the base material is selected from one or more elemental metals such as nickel, cobalt, palladium, copper, and chromium, or from one or more alloy materials such as nickel-chromium alloy, nickel-cobalt alloy, and nickel-copper alloy. The total thickness of the base layer is 0.1μm to 5μm.

4. The method for vapor deposition-thermal diffusion composite coating of metal wire surface according to claim 1, characterized in that: In step three, the high-melting-point metal functional layer material is selected from one pure metal or its alloy from titanium, tungsten, molybdenum, niobium, and zirconium; The thickness of the high-melting-point metal functional layer ranges from 1 μm to 50 μm, and the thickness uniformity is controlled within ±5% of the average thickness.

5. The method for vapor deposition-thermal diffusion composite coating of metal wire surface according to claim 1, characterized in that: In step four, the temperature for low-temperature thermal diffusion treatment is 400°C to 900°C, and the holding time is 30 min to 300 min. When the metal wire substrate is titanium or titanium alloy and the functional layer is tungsten or molybdenum, the thermal diffusion temperature is preferably 500°C to 700°C. When the metal wire substrate is tungsten or molybdenum and the functional layer is titanium or zirconium, the thermal diffusion temperature is preferably 600°C to 800°C.

6. The method for vapor deposition-thermal diffusion composite coating of metal wire surface according to claim 5, characterized in that: In step four, the heating rate of the low-temperature thermal diffusion treatment is 2°C / min to 15°C / min, and the cooling rate is 1°C / min to 10°C / min. The heating process adopts a segmented control method, first holding at 200°C to 300°C for 10 to 30 minutes, and then heating up to the target diffusion temperature.

7. The method for vapor deposition-thermal diffusion composite coating of metal wire surface according to claim 1, characterized in that: In step four, the vacuum level of the vacuum environment is less than or equal to 1.0 × 10⁻⁶. -2 Pa; The protective atmosphere is argon, helium or nitrogen with a purity of not less than 99.99%, and the furnace pressure is controlled at 0.1 atm to 0.8 atm.

8. The method for vapor deposition-thermal diffusion composite coating of metal wire surface according to claim 1, characterized in that: The surface pretreatment in step one includes electrolytic degreasing, acid pickling and activation, ultrasonic cleaning and glow discharge cleaning; The current density for electrolytic degreasing is 2 A / dm. 2 Up to 10A / dm 2 The processing time is 30 to 180 seconds; The glow discharge cleaning voltage is 500V to 1000V, and the processing time is 5min to 20min. After pretreatment, the surface cleanliness of the metal wire substrate reaches over 95%.

9. The method for vapor deposition-thermal diffusion composite coating of metal wire surface according to claim 1, characterized in that: The post-processing in step five includes surface brightening, sizing drawing, and stress-relief annealing; Surface brightening treatment is achieved through chemical polishing or electrochemical polishing; The stress-relief annealing temperature is 200°C to 400°C, and the holding time is 30 min to 120 min; The total deformation during sizing drawing is 10% to 30%.

10. The method for vapor deposition-thermal diffusion composite coating of metal wire surface according to claim 1, characterized in that: The metal wire substrate is a continuous slender wire made of one of the following: steel, stainless steel, copper and copper alloys, nickel and nickel alloys, titanium and titanium alloys, tungsten and tungsten alloys, molybdenum and molybdenum alloys. Its original diameter is 0.01 mm to 5 mm and the length-to-diameter ratio is greater than 1000:1.

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