Plating process of titanium wire surface coating

Abstract

The invention discloses a plating process of a titanium wire surface coating, which comprises the following steps: S1, composite pretreatment, including alkaline degreasing, pickling and pulse laser scanning; s2, chemically plating a transition layer; s3, performing pulse electrocoating on the functional layer; and S4, performing low-temperature densification treatment. A micro-nano coarse structure is constructed by innovatively adopting pulse laser, so that interface bonding is enhanced to prevent the coating from falling off; a gradient structure of a nickel-phosphorus transition layer and a nickel-tungsten functional layer of silane modified nano aluminum oxide is designed, so that the comprehensive properties such as wear resistance and high temperature resistance are improved; chemical plating and pulse electroplating are matched with low-temperature densification, equipment investment and energy consumption are reduced, the period is shortened, and both efficiency and environmental protection are considered. The coating obtained by the plating process of the titanium wire surface coating has high-strength binding force, high hardness and high temperature resistance, and the process is environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, and in particular to a coating process for titanium wire surfaces. Background Technology

[0002] Titanium wire is widely used in many high-end fields due to its excellent corrosion resistance, biocompatibility, and high strength-to-weight ratio. However, pure titanium wire has low surface hardness, poor wear resistance, and is prone to oxidation failure at high temperatures, which limits its application range in extreme working conditions.

[0003] Existing surface treatment technologies such as laser cladding are prone to cracking, and high carbon content leads to interfacial stress concentration and reduced toughness. Cold spraying requires expensive gases and has high porosity, while traditional electroplating suffers from weak adhesion due to oxide film interference. Ion plating, such as multi-arc ion plating, suffers from insufficient film-substrate adhesion and is prone to peeling. Surface diffusion methods, such as combining high-temperature treatment of aluminum alloys with electromagnetic cooling, are prone to pores and cracks in the coating. These methods generally suffer from weak coating adhesion, poor microstructure uniformity, or high process complexity, and the interfacial bonding between the coating and the substrate, as well as high-temperature resistance, still need to be optimized.

[0004] Therefore, there is an urgent need to develop a coating process for titanium wire surfaces that combines high bonding strength, high hardness, high temperature resistance, and environmental friendliness. Summary of the Invention

[0005] The purpose of this invention is to provide a coating process for titanium wire surfaces to solve the problems of weak coating adhesion, poor microstructure uniformity, or high process complexity in existing titanium wire surface treatment processes.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A coating process for a titanium wire surface includes the following steps:

[0008] S1. Composite pretreatment: The titanium wire is placed in an alkaline degreasing solution and ultrasonically cleaned at 50~60℃. After ultrasonic cleaning, it is rinsed with deionized water. Then, the degreased titanium wire is immersed in a pickling mixture with a mass fraction of 10~15% for pickling. After pickling, it is rinsed with deionized water. The surface of the titanium wire is scanned using a pulsed laser to obtain the pretreated titanium wire.

[0009] S2. Transition layer chemical plating: The pretreated titanium wire is placed in the chemical plating solution and kept at 85~90℃ for 40~60min to form a nickel-phosphorus transition layer.

[0010] S3. Functional layer pulse electroplating: A titanium wire coated with a transition layer is used as the cathode and graphite as the anode. The wire is placed in a composite plating solution for pulse electroplating and ultrasonic dispersion to form a nickel-tungsten-nano Al2O3 functional layer.

[0011] S4. Low-temperature densification treatment: The coated titanium wire is placed in a vacuum furnace and held at 300~350℃ for 2~3 hours, with a vacuum degree of... The titanium wire is then cooled to room temperature in the furnace, and a composite coating is formed on the surface of the titanium wire.

[0012] As a preferred embodiment of the present invention, in step S1:

[0013] The alkaline degreasing solution is prepared in the following proportions by weight: 5-8 parts sodium hydroxide, 3-5 parts sodium carbonate, 1-2 parts surfactant sodium dodecylbenzene sulfonate, and 85-90 parts water;

[0014] The ultrasonic frequency is 20~40kHz, and the ultrasonic time is 15~20min;

[0015] The mass ratio of hydrofluoric acid to nitric acid in the pickling mixture is 1:3.

[0016] The pulsed laser has a power of 50~80W, a scanning speed of 100~150mm / s, and a pulse frequency of 20~30kHz.

[0017] As a preferred embodiment of the present invention, in step S2, the chemical plating solution is prepared in the following weight proportions: 25-30 parts nickel sulfate, 35-40 parts sodium hypophosphite, 15-20 parts sodium citrate, 10-15 parts ammonium chloride, and 910-930 parts water.

[0018] As a preferred embodiment of the present invention, in step S3, the composite plating solution is prepared in the following weight proportions: 40-50 parts nickel sulfate, 20-25 parts sodium tungstate, 5-8 parts modified nano alumina, 25-30 parts trisodium citrate, 10-15 parts boric acid, and 870-900 parts water.

[0019] As a preferred embodiment of the present invention, in step S3, the pulse parameters are: forward pulse current density of 3~5A / dm², pulse width of 200~300μs, reverse pulse current density of 1~2A / dm², pulse width of 50~100μs, electroplating temperature of 55~60℃, and time of 60~90min.

[0020] In a preferred embodiment of the present invention, in step S3, the frequency of the ultrasonic dispersion is 30-40 kHz and the ultrasonic power is 200-400 W.

[0021] As a preferred technical solution of the present invention, the preparation method of the modified nano-alumina is as follows: nano-Al2O3 particles with a particle size of 50~80nm are taken and mixed with anhydrous ethanol at a mass ratio of 10~20:1. Then, the mixture is ultrasonically dispersed for 20~30min at an ultrasonic frequency of 20~30kHz to obtain a suspension. Next, silane coupling agent KH550 is added at 1~3% of the mass of nano-Al2O3. The mixture is stirred and reacted at 50~60℃ for 30~40min. Then, the mixture is centrifuged at 3000~6000rpm to separate the precipitate. The precipitate is dried at 80~100℃ for 2~3h to obtain modified nano-alumina.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. The composite pretreatment in this invention serves as the primary step in the titanium wire surface coating process, laying a core foundation for the subsequent coating quality. The alkaline degreasing solution, under ultrasonic assistance, efficiently removes organic impurities such as grease and dust. The subsequent acid pickling mixture selectively removes oxide scale while preventing over-corrosion of the titanium substrate. This dual treatment ensures no impurities remain on the surface. Simultaneously, pulsed laser scanning constructs the surface morphology and optimizes active sites. Under laser irradiation, a micro-nano-level rough structure forms on the titanium wire surface, significantly increasing the specific surface area. Furthermore, the laser energy excites surface atomic activity, breaking the constraints of the original inert oxide layer and forming a highly active surface. This modification effect allows the subsequent nickel-phosphorus transition layer to achieve significantly enhanced bonding strength during chemical plating through the mechanical interlocking of the rough surface and the chemical adsorption of active sites, avoiding the risk of coating peeling. In addition, alkaline degreasing provides a clean substrate for pickling, ensuring uniform removal of oxide scale; laser scanning is performed on a clean surface, avoiding morphological inconsistencies caused by impurities. The three-step process ensures a highly consistent surface state of the titanium wire, providing a uniform reaction substrate for subsequent gradient plating and low-temperature densification, ultimately improving the overall density and performance stability of the composite coating, and fully guaranteeing the coating's wear resistance, corrosion resistance, and other functions.

[0024] 2. This invention achieves a gradient composite coating through a combination of chemical plating and pulse electrocoating. The nickel-phosphorus transition layer formed by chemical plating, leveraging the uniformity of chemical deposition, can adhere tightly to the pretreated titanium wire surface, filling the gaps in the micro / nano rough structure. Simultaneously, its chemical activity provides a suitable substrate for the subsequent adhesion of functional layers, solving the problem of easy detachment between the titanium substrate and the functional layer. The nickel-tungsten-nano Al2O3 functional layer constructed by pulse electrocoating, through the alternating action of positive and negative pulses, suppresses coarse grain growth in the coating, while ultrasonic dispersion ensures a dense and uniform coating. The high hardness of the nickel-tungsten alloy combined with the reinforcing effect of the nanoparticles imparts excellent wear resistance and corrosion resistance to the coating.

[0025] 3. This invention improves the dispersibility and binding force of nano-Al2O3 by modifying it. Unmodified particles are prone to agglomeration, resulting in uneven coating performance. However, after modification with silane coupling agent KH550, one end of the coupling agent molecule binds to the nanoparticles, and the other end forms a chemical bond with the plating solution and coating. This achieves stable dispersion in the composite plating solution and enhances the interfacial bonding between the particles and the nickel-tungsten matrix, preventing particle detachment and failure during service. This makes the coating strengthening effect more durable and stable, and the two work together to ensure the comprehensive performance of the composite coating. Attached Figure Description

[0026] Figure 1 This is a flow chart of the titanium wire surface coating process of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Pulsed lasers offer precise and controllable parameters, along with a gentle yet highly efficient effect. Through precise optimization of surface modification, they can construct micro-nano morphologies suitable for coating. Under the influence of laser energy, a uniform micro-nano rough structure forms on the surface of the titanium wire, increasing the specific surface area and providing "anchor points" for mechanical interlocking in the subsequent nickel-phosphorus transition layer. Simultaneously, it activates surface chemical activity; the laser energy can break the stable structure of the inert oxide layer on the titanium wire surface, stimulate surface atomic activity, increase chemical adsorption sites, and strengthen the chemical bonding force with the transition layer. Furthermore, it ensures consistent processing; pulsed scanning ensures that energy is applied uniformly to the titanium wire surface, avoiding localized over-etching or uneven modification. Combined with a clean substrate obtained through pre-degreasing and pickling, it ensures a uniform surface condition of the titanium wire, laying the foundation for the uniformity of subsequent gradient coating and ultimately improving the overall bonding stability of the composite coating.

[0029] The core characteristic of electroless plating is that it requires no external power source, relying on the chemical reaction of the plating solution to achieve deposition. The plating solution is a compound of nickel sulfate, sodium hypophosphite, etc., which has both autocatalytic properties and uniformity. With the help of uniform deposition characteristics, a dense nickel-phosphorus transition layer can be formed on the surface of titanium wire, filling the micro-nano rough structure after pretreatment. Its chemical activity enables the transition layer to form a strong chemical bond with the titanium substrate, while providing a suitable substrate for subsequent functional layers, solving the problem of coating peeling caused by the inertness of the titanium substrate.

[0030] Pulsed electrocoating, powered by pulsed current, employs alternating forward and reverse pulses combined with ultrasonic dispersion. This provides controllable energy and a grain refinement effect, enabling precise introduction of nanoparticles. The pulsed current suppresses grain coarsening, while ultrasonic dispersion ensures uniform distribution of nano-Al2O3, resulting in a high-density nickel-tungsten-nano-Al2O3 functional layer. The high hardness of the nickel-tungsten alloy, combined with the dispersion reinforcement of nanoparticles, significantly improves the coating's wear resistance and corrosion resistance. The gentle electroplating process at 55~60℃ avoids damage to the substrate properties.

[0031] By synergistically combining the two gradients, the transition layer obtained by electroless plating solves the "bonding bottleneck," while the functional layer obtained by pulse electroplating ensures the "performance peak," forming a hierarchical structure of "strong bonding and high functionality." The uniformity of electroless plating provides a uniform substrate for pulse electroplating, avoiding uneven thickness of the functional layer. The precise control of pulse electroplating compensates for the deficiency of hardness in electroless plating, enabling the composite coating to have both strong bonding with the substrate and excellent service performance, adapting to the requirements of harsh working conditions.

[0032] This invention adds nano-Al2O3 to the composite plating solution and precisely controls its particle size to 50~80nm, which has extremely strong dispersion strengthening potential. At the same time, nano-alumina itself has extremely high hardness and chemical stability. As ceramic phase particles, it can endow the coating with excellent wear resistance and corrosion resistance. In addition, there are a large number of hydroxyl groups on the surface of nano-alumina, which are highly polar. However, due to its extremely high surface energy, it is easy to agglomerate when untreated, making it difficult to disperse evenly in the plating solution. Moreover, it has poor compatibility with the metal substrate interface, and direct addition can easily lead to uneven coating performance. After modification with silane coupling agent KH550, one end of the coupling agent molecule binds to the hydroxyl groups on the surface of nano-Al2O3 via chemical bonds, while the other end exhibits organophilic properties, making it compatible with organic components and the nickel-tungsten alloy matrix in the plating bath. Combined with purification treatment through centrifugation and drying, it effectively disperses agglomerates, ensuring stable dispersion in the composite plating bath. Simultaneously, it strengthens interfacial bonding; the "bridge" effect formed by the coupling agent enables chemical bonding between the nanoparticles and the nickel-tungsten matrix, replacing simple physical embedding and preventing particles from detaching from the matrix during service, thus solving the problem of inorganic particle... Addressing the industry pain point of weak bonding between particles and the metal substrate; and maximizing the strengthening effect, uniformly dispersed modified nano-Al2O3 forms a dense co-deposited layer with nickel-tungsten alloy during pulse electrocoating. The 50~80nm particle size can refine the coating grains, and combined with the high hardness of the nickel-tungsten alloy itself, the wear resistance of the coating is significantly improved compared with the unmodified particle coating. At the same time, its chemical stability can enhance the corrosion resistance of the coating. Combined with the ultrasonic dispersion synergistic effect of pulse electrocoating, the synergistic effect of "uniform dispersion - strong bonding - high-efficiency strengthening" is finally achieved, ensuring that the performance of the functional layer meets the standards.

[0033] like Figure 1 As shown, a coating process for a titanium wire surface includes the following steps:

[0034] S1. Composite pretreatment: The titanium wire is placed in an alkaline degreasing solution and ultrasonically cleaned at 50~60℃. After ultrasonic cleaning, it is rinsed with deionized water. Then, the degreased titanium wire is immersed in a pickling mixture with a mass fraction of 10~15% for pickling. After pickling, it is rinsed with deionized water. The surface of the titanium wire is scanned using a pulsed laser to obtain the pretreated titanium wire.

[0035] S2. Transition layer chemical plating: The pretreated titanium wire is placed in the chemical plating solution and kept at 85~90℃ for 40~60min to form a nickel-phosphorus transition layer;

[0036] S3. Functional layer pulse electroplating: A titanium wire coated with a transition layer is used as the cathode and graphite as the anode. The wire is placed in a composite plating solution for pulse electroplating and ultrasonic dispersion to form a nickel-tungsten-nano Al2O3 functional layer.

[0037] S4. Low-temperature densification treatment: The coated titanium wire is placed in a vacuum furnace and held at 300~350℃ for 2~3 hours, with a vacuum degree of... The titanium wire is then cooled to room temperature in the furnace, and a composite coating is formed on the surface of the titanium wire.

[0038] All raw materials used in this invention are commercially available.

[0039] Example 1:

[0040] A coating process for a titanium wire surface includes the following steps:

[0041] S1. Composite Pretreatment: The titanium wire was placed in an alkaline degreasing solution (prepared by weight: 8 parts sodium hydroxide, 5 parts sodium carbonate, 2 parts sodium dodecylbenzenesulfonate surfactant, and 90 parts water), and ultrasonically cleaned for 20 minutes at 60°C and an ultrasonic frequency of 40 kHz. After ultrasonic cleaning, it was rinsed with deionized water. Then, the degreased titanium wire was immersed in a 15% (w / w) pickling mixture (where the mass ratio of hydrofluoric acid to nitric acid was 1:3) at room temperature for 5 minutes. After pickling, it was rinsed with deionized water. The surface of the titanium wire was then scanned using a pulsed laser with a power of 80 W, a scanning speed of 150 mm / s, and a pulse frequency of 30 kHz to obtain the pretreated titanium wire.

[0042] S2. Transition layer chemical plating: The pretreated titanium wire is placed in a chemical plating solution (prepared by weight: 30 parts nickel sulfate, 40 parts sodium hypophosphite, 20 parts sodium citrate, 15 parts ammonium chloride, and 930 parts water) and kept at 90°C for 60 minutes to form a nickel-phosphorus transition layer.

[0043] S3. Functional Layer Pulse Electroplating: A titanium wire coated with a transition layer is used as the cathode and graphite as the anode. The wire is placed in a composite plating solution (prepared by weight: 50 parts nickel sulfate, 25 parts sodium tungstate, 8 parts modified nano alumina, 30 parts trisodium citrate, 15 parts boric acid, and 900 parts water). Pulse electroplating is performed for 90 minutes at a forward pulse current density of 5 A / dm², a pulse width of 300 μs, a reverse pulse current density of 2 A / dm², a pulse width of 100 μs, and a plating temperature of 60℃. Simultaneously, ultrasonic dispersion is performed at a frequency of 40 kHz and an ultrasonic power of 400 W to form a nickel-tungsten-nano Al2O3 functional layer.

[0044] The preparation method of modified nano-alumina is as follows: nano-Al2O3 particles with a particle size of 50~80nm are taken and mixed with anhydrous ethanol at a mass ratio of 20:1. Then, the mixture is ultrasonically dispersed for 30min at an ultrasonic frequency of 30kHz to obtain a suspension. Next, silane coupling agent KH550 is added at 3% of the mass of nano-Al2O3. The mixture is stirred and reacted at 60℃ for 40min. After stirring, the mixture is centrifuged at 6000rpm and the precipitate is separated. The precipitate is dried at 100℃ for 3h to obtain modified nano-alumina.

[0045] S4. Low-temperature densification treatment: The coated titanium wire is placed in a vacuum furnace and held at 350℃ for 3 hours, with a vacuum degree of... The titanium wire is then cooled to room temperature in the furnace, and a composite coating is formed on the surface of the titanium wire.

[0046] Example 2:

[0047] A coating process for a titanium wire surface includes the following steps:

[0048] S1. Composite Pretreatment: The titanium wire was placed in an alkaline degreasing solution (prepared by weight: 6 parts sodium hydroxide, 4 parts sodium carbonate, 1.5 parts sodium dodecylbenzenesulfonate surfactant, and 87 parts water), and ultrasonically cleaned for 17 minutes at 55°C and an ultrasonic frequency of 30 kHz. After ultrasonic cleaning, it was rinsed with deionized water. Then, the degreased titanium wire was immersed in a 12.5% ​​(by mass) pickling mixture (in which the mass ratio of hydrofluoric acid to nitric acid was 1:3) at room temperature for 4 minutes. After pickling, it was rinsed with deionized water. The surface of the titanium wire was then scanned using a pulsed laser with a power of 65 W, a scanning speed of 125 mm / s, and a pulse frequency of 25 kHz to obtain the pretreated titanium wire.

[0049] S2. Transition layer chemical plating: The pretreated titanium wire is placed in a chemical plating solution (prepared by weight: 27 parts nickel sulfate, 37 parts sodium hypophosphite, 17 parts sodium citrate, 12 parts ammonium chloride, and 920 parts water) and kept at 87.5℃ for 50 minutes to form a nickel-phosphorus transition layer.

[0050] S3. Functional Layer Pulse Electroplating: A titanium wire coated with a transition layer is used as the cathode and graphite as the anode. The wire is placed in a composite plating solution (prepared in the following weight parts: 45 parts nickel sulfate, 22 parts sodium tungstate, 7 parts modified nano alumina, 27 parts trisodium citrate, 12 parts boric acid, and 885 parts water). Pulse electroplating is performed for 75 minutes at a forward pulse current density of 4 A / dm², a pulse width of 250 μs, a reverse pulse current density of 1.5 A / dm², a pulse width of 75 μs, and a plating temperature of 57.5℃. Simultaneously, ultrasonic dispersion is performed at a frequency of 35 kHz and an ultrasonic power of 300 W to form a nickel-tungsten-nano Al2O3 functional layer.

[0051] The preparation method of modified nano-alumina is as follows: nano-Al2O3 particles with a particle size of 50~80nm are taken and mixed with anhydrous ethanol at a mass ratio of 15:1. Then, the mixture is ultrasonically dispersed for 25min at an ultrasonic frequency of 25kHz to obtain a suspension. Next, silane coupling agent KH550 is added at 2% of the mass of nano-Al2O3. After stirring and reacting at 55℃ for 35min, the mixture is centrifuged at 4500rpm and the precipitate is separated. The precipitate is dried at 90℃ for 2.5h to obtain modified nano-alumina.

[0052] S4. Low-temperature densification treatment: The coated titanium wire is placed in a vacuum furnace and kept at 325℃ for 2.5h with a vacuum degree ≤5×10⁻³Pa. Then it is cooled to room temperature with the furnace, and a composite coating is formed on the surface of the titanium wire.

[0053] Example 3:

[0054] A coating process for a titanium wire surface includes the following steps:

[0055] S1. Composite Pretreatment: The titanium wire was placed in an alkaline degreasing solution (prepared by weight: 5 parts sodium hydroxide, 3 parts sodium carbonate, 1 part sodium dodecylbenzenesulfonate surfactant, and 85 parts water), and ultrasonically cleaned for 15 minutes at 50°C and an ultrasonic frequency of 20 kHz. After ultrasonic cleaning, it was rinsed with deionized water. Then, the degreased titanium wire was immersed in a 10% (w / w) pickling mixture (where the mass ratio of hydrofluoric acid to nitric acid was 1:3) at room temperature for 3 minutes. After pickling, it was rinsed with deionized water. The surface of the titanium wire was then scanned using a pulsed laser with a power of 50 W, a scanning speed of 100 mm / s, and a pulse frequency of 20 kHz to obtain the pretreated titanium wire.

[0056] S2. Transition layer chemical plating: The pretreated titanium wire is placed in a chemical plating solution (prepared by weight: 25 parts nickel sulfate, 35 parts sodium hypophosphite, 15 parts sodium citrate, 10 parts ammonium chloride, and 910 parts water) and kept at 85°C for 40 minutes to form a nickel-phosphorus transition layer.

[0057] S3. Functional Layer Pulse Electroplating: A titanium wire coated with a transition layer is used as the cathode and graphite as the anode. The wire is placed in a composite plating solution (prepared by weight: 40 parts nickel sulfate, 20 parts sodium tungstate, 5 parts modified nano alumina, 25 parts trisodium citrate, 10 parts boric acid, and 870 parts water). Pulse electroplating is performed for 60 minutes at a forward pulse current density of 3 A / dm², a pulse width of 200 μs, a reverse pulse current density of 1 A / dm², a pulse width of 50 μs, and a plating temperature of 55℃. Simultaneously, ultrasonic dispersion is performed at a frequency of 30 kHz and an ultrasonic power of 200 W to form a nickel-tungsten-nano Al2O3 functional layer.

[0058] The preparation method of modified nano-alumina is as follows: nano-Al2O3 particles with a particle size of 50~80nm are taken and mixed with anhydrous ethanol at a mass ratio of 10:1. Then, the mixture is ultrasonically dispersed for 20min at an ultrasonic frequency of 20kHz to obtain a suspension. Then, silane coupling agent KH550 is added at 1% of the mass of nano-Al2O3. After stirring and reacting at 50℃ for 30min, the mixture is centrifuged at 3000rpm and the precipitate is separated. The precipitate is dried at 80℃ for 2h to obtain modified nano-alumina.

[0059] S4. Low-temperature densification treatment: The coated titanium wire is placed in a vacuum furnace and kept at 300℃ for 2 hours with a vacuum degree ≤5×10⁻³Pa. Then it is cooled to room temperature with the furnace, and a composite coating is formed on the surface of the titanium wire.

[0060] Comparative Example 1:

[0061] The difference from Example 1 is that the pulsed laser treatment in the S1 composite pretreatment is replaced with traditional sandblasting treatment (where the sandblasting medium is 80-mesh zirconium corundum sand, the pressure is 0.4MPa, and the treatment time is 3min).

[0062] Comparative Example 2:

[0063] The difference from Example 1 is that nano-alumina is added directly to the composite plating solution without modification.

[0064] Comparative Example 3:

[0065] The difference from Example 1 is that the S2 chemical plating step is removed.

[0066] Comparative Example 4:

[0067] The difference from Example 1 is that steps S2 and S3 are replaced with a single acidic electroplating nickel-tungsten process.

[0068] The performance of the titanium wire surface coatings obtained in Examples 1, 2, and 3, and Comparative Examples 1, 2, 3, and 4 was tested. Peel strength was tested according to standard GB / T5270-2005 "Review of Test Methods for Adhesion Strength of Electrodeposited and Chemically Deposited Metallic Coatings on Metallic Substrates"; micro hardness (HV) was tested using a micro Vickers hardness tester according to standard GB / T4340.1-2009 "Vickers Hardness Test of Metallic Materials"; and high-temperature resistance was tested according to standard GB / T42259-2022 "Test Methods for Thermal Barrier Coatings of Metals and Other Inorganic Coatings - Thermal Cycling and Thermal Shock Resistance". One cycle consisted of standing at 400℃ for 10 minutes followed by standing at room temperature for 10 minutes, and a total of 100 cycles were performed. The coating condition was observed after the cycles. The test results are shown in Table 1.

[0069] Table 1: Performance tests of coatings prepared in the examples and comparative examples

[0070]

[0071] As can be seen from Table 1, the surface coating prepared in the embodiment group of the present invention has stronger adhesion, higher hardness, and better high temperature resistance compared to the comparative example group.

[0072] Pulsed laser pretreatment creates a micro-nano rough surface, providing mechanical interlocking "anchors" for subsequent coatings. Simultaneously, it activates the atomic activity of the titanium wire surface, significantly enhancing the chemical adsorption between the coating and the substrate, and substantially improving peel strength. Its uniform modification effect lays the foundation for coating uniformity and indirectly optimizes stress distribution at high temperatures. The nickel-phosphorus transition layer in S2 electroless plating acts as a "bridge," tightly adhering to the pretreated surface and filling micro-gaps, completely resolving the bonding bottleneck between the titanium substrate and the functional layer, and improving peel strength. The compatibility of the transition layer with the substrate and functional layer alleviates thermal stress during high-temperature cycling, enhancing high-temperature stability. Modified nano-Al2O3 in the composite plating solution, after treatment with a coupling agent, exhibits improved dispersion and interfacial bonding; its dispersion strengthening effect significantly improves coating hardness. Uniformly distributed nanoparticles refine grains, reducing crack initiation at high temperatures. S3 pulse electrocoating employs forward pulse deposition and reverse pulse grain refinement, combined with ultrasonic dispersion, to achieve a dense and uniform coating, thus improving both peel strength and hardness. Furthermore, the gentle processing and dense coating structure prevent high-temperature oxidation and inhibit grain coarsening, enhancing high-temperature resistance. The synergistic effect of these steps results in a coating with stable peel strength, excellent hardness, and the ability to withstand repeated thermal cycling, achieving satisfactory overall performance. In addition, this invention features a high proportion of low-temperature operations. Low-temperature densification and pulse electrocoating performed at 55-60°C significantly reduce energy consumption and emissions compared to higher-temperature processes. Simultaneously, the reagents are highly efficient and low-consumption; the modified nano-Al2O3 exhibits good dispersibility and requires minimal dosage, reducing solid waste generation. Moreover, the use of deionized water for cleaning ensures precise formulation of the plating solution, minimizing impurity introduction and reducing the burden on subsequent wastewater treatment, thus meeting clean production requirements.

[0073] In summary, the coating obtained by the titanium wire surface coating process of the present invention has the advantages of high bonding strength, high hardness, high temperature resistance, and environmentally friendly process.

[0074] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A coating process for a titanium wire surface, characterized in that, The process includes three steps: composite pretreatment, gradient composite coating, and low-temperature densification treatment. The specific steps are as follows: S1. Composite pretreatment: The titanium wire is placed in an alkaline degreasing solution and ultrasonically cleaned at 50~60℃. After ultrasonic cleaning, it is rinsed with deionized water. Then, the degreased titanium wire is immersed in a pickling mixture with a mass fraction of 10~15% and soaked at room temperature for 3~5 minutes. After pickling, it is rinsed with deionized water. The surface of the titanium wire is scanned using a pulsed laser to obtain the pretreated titanium wire. S2. Transition layer chemical plating: The pretreated titanium wire is placed in the chemical plating solution and kept at 85~90℃ for 40~60min to form a nickel-phosphorus transition layer; S3. Functional layer pulse electroplating: A titanium wire coated with a transition layer is used as the cathode and graphite as the anode. The wire is placed in a composite plating solution for pulse electroplating and ultrasonic dispersion to form a nickel-tungsten-nano Al2O3 functional layer. S4. Low-temperature densification treatment: The coated titanium wire is placed in a vacuum furnace and kept at 300~350℃ for 2~3 hours with a vacuum degree ≤5×10⁻³Pa. Then it is cooled to room temperature with the furnace, and a composite coating is formed on the surface of the titanium wire.

2. The coating process for a titanium wire surface coating according to claim 1, characterized in that, In S1: The alkaline degreasing solution is prepared in the following proportions by weight: 5-8 parts sodium hydroxide, 3-5 parts sodium carbonate, 1-2 parts surfactant sodium dodecylbenzene sulfonate, and 85-90 parts water; The ultrasonic frequency is 20~40kHz, and the ultrasonic time is 15~20min; The mass ratio of hydrofluoric acid to nitric acid in the pickling mixture is 1:

3. The pulsed laser has a power of 50~80W, a scanning speed of 100~150mm / s, and a pulse frequency of 20~30kHz.

3. The coating process for a titanium wire surface coating according to claim 1, characterized in that, In step S2, the chemical plating solution is prepared in the following weight proportions: 25-30 parts nickel sulfate, 35-40 parts sodium hypophosphite, 15-20 parts sodium citrate, 10-15 parts ammonium chloride, and 910-930 parts water.

4. The coating process for a titanium wire surface coating according to claim 1, characterized in that, In S3, the composite plating solution is prepared in the following weight parts: 40-50 parts nickel sulfate, 20-25 parts sodium tungstate, 5-8 parts modified nano alumina, 25-30 parts trisodium citrate, 10-15 parts boric acid, and 870-900 parts water.

5. The coating process for a titanium wire surface coating according to claim 1, characterized in that, In S3, the pulse parameters are: forward pulse current density of 3~5A / dm², pulse width of 200~300μs, reverse pulse current density of 1~2A / dm², pulse width of 50~100μs, electroplating temperature of 55~60℃, and time of 60~90min.

6. The coating process for a titanium wire surface coating according to claim 1, characterized in that, In step S3, the frequency of the ultrasonic dispersion is 30~40kHz, and the ultrasonic power is 200~400W.

7. The coating process for a titanium wire surface coating according to claim 4, characterized in that, The modified nano-alumina is prepared as follows: nano-Al2O3 particles with a particle size of 50-80 nm are taken and mixed with anhydrous ethanol at a mass ratio of 10-20:

1. The mixture is then ultrasonically dispersed at an ultrasonic frequency of 20-30 kHz for 20-30 min to obtain a suspension. Then, silane coupling agent KH550 is added at 1-3% of the mass of nano-Al2O3. The mixture is stirred and reacted at 50-60℃ for 30-40 min. After stirring, the mixture is centrifuged at 3000-6000 rpm to separate the precipitate. The precipitate is dried at 80-100℃ for 2-3 h to obtain modified nano-alumina.

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