A micro-arc oxidation composite coating of TC4 titanium alloy based on laser texturing cooperation and an in-situ growth-composite sealing method thereof

Abstract

The application discloses a TC4 titanium alloy micro-arc oxidation composite coating based on laser texturing cooperation and an in-situ growth-composite sealing hole preparation method thereof; the four-step continuous cooperation process of "ultrafast laser micro-texture construction-gradient voltage micro-arc oxidation film formation-surface hydroxylation activation-silane / nano silicon nitride composite sealing hole solidification"; wherein, the laser texture provides a micro anchor structure; the gradient micro-arc oxidation forms a dense ceramic bottom layer mainly composed of TiO2; the hydroxylation activation introduces active bonding sites on the surface of the ceramic layer; and the sol compounded of hexadecyl trimethoxysilane and nano silicon nitride deeply penetrates into the pores and forms a composite sealing hole layer with hydrophobic and wear-resistant reinforcing functions after solidification. The composite coating significantly improves the long-term corrosion resistance of the TC4 titanium alloy in a corrosion medium containing chlorine ions, the wear resistance under friction conditions, and endows the TC4 titanium alloy with a stable super-hydrophobic surface; and is suitable for surface protection of TC4 titanium alloy components in harsh environments of corrosion-wear coupling.

Description

Technical Field

[0001] This invention belongs to the field of surface functionalization and composite modification technology of metallic materials, specifically involving a micro-arc oxidation composite coating of TC4 titanium alloy based on laser texturing synergy and its in-situ growth-composite sealing method. The preparation method uses a multi-step synergy of ultrafast laser texturing, micro-arc oxidation, hydroxyl activation and silane / nanoparticle composite sealing to construct a composite coating on the surface of TC4 titanium alloy with high density, strong adhesion, excellent hydrophobicity and wear and corrosion resistance. Background Technology

[0002] TC4 (Ti-6Al-4V) titanium alloy has become a key structural material in aerospace, marine engineering, and high-end equipment manufacturing due to its high specific strength, good biocompatibility, and inherent corrosion resistance in various media. However, its relatively low surface hardness (approximately 300-400 HV) and poor wear resistance, especially in complex working conditions involving chloride-containing media (such as seawater and salt spray) coupled with friction and fretting, easily induce severe wear-corrosion interaction damage, leading to premature component failure and limiting its long-term reliable application in critical load-bearing components.

[0003] To improve the surface properties of TC4 titanium alloy, existing technologies have developed a variety of surface modification paths: (1) Physical vapor deposition (PVD) and thermal spraying technology: hard coatings such as TiN and CrN or ceramic coatings can be deposited on the surface, which can significantly improve the surface hardness and wear resistance. However, these technologies usually have problems such as limited bonding strength between the coating and the substrate (especially for complex shaped components), high process temperature which can easily cause thermal deformation or phase transformation of the substrate, and micropores or interlayer defects in the coating. More importantly, when such "external" coatings are used in corrosive media for a long time, once the medium penetrates to the interface through defects, it is very easy to cause the coating to blister and peel off, resulting in the instantaneous loss of protective function and making it difficult to meet the long-term corrosion resistance requirements. (2) Micro-arc oxidation technology: This technology can grow a ceramic oxide layer with TiO2 as the main component and metallurgical bonding with the substrate on the surface of titanium alloy. While improving the surface hardness, it provides good chemical inertness and electrical insulation, which is one of the effective means to achieve integrated wear resistance and corrosion resistance. However, the inherent porous structure (porosity typically between 5% and 15%) and microcracks of the micro-arc oxide layer constitute a corrosive medium (such as Cl). -) Rapid channels for migration to the coating / substrate interface. Under long-term static or dynamic friction, the medium penetration intensifies, causing interface corrosion and coating adhesion degradation, ultimately leading to protection failure. This "pore penetration" problem has become the core bottleneck restricting the long-term protective capability of micro-arc oxidation coatings. (3) Micro-arc oxidation post-sealing technology: In order to overcome the above-mentioned pore problem, researchers often use post-treatment processes such as silanization, sol-gel or polymer impregnation to seal the pores. For example, treatment with a single silane (such as methyltrimethoxysilane) can form a hydrophobic film on the coating surface, which to a certain extent blocks the direct contact of the medium. However, this type of method has obvious limitations: (a) The sealing agent mainly covers the surface of the coating and is difficult to penetrate deep into the interior of the coating and the bottom of the microcracks, resulting in "shallow sealing". Under long-term service, the medium can still penetrate in a roundabout way; (b) The single organic sealing layer has low mechanical strength and poor wear resistance. It is easily worn and failed under friction conditions, losing its sealing and hydrophobic functions; (c) If there is a lack of strong chemical bonding between the sealing layer and the micro-arc oxidation ceramic layer, the interfacial bonding force is weak and it is easy to peel off under thermal cycling or stress. (4) Surface texture and composite strengthening technology: Recently, some studies have attempted to perform laser texture on the substrate before micro-arc oxidation to increase the surface area, improve coating adhesion, or store lubricant. Some studies have also attempted to add nanoparticles (such as Al2O3, SiO2) to the electrolyte or to perform nanoparticle composite sealing on the micro-arc oxidation coating. However, existing technical solutions often exhibit the characteristics of "isolated optimization": they may focus on improving the bonding force through texture but fail to systematically solve the problem of pore sealing; they may focus on introducing nanoparticles but fail to effectively activate the coating surface to achieve strong particle bonding; or they may fail to construct a complete and synergistic technical chain from "matrix texture → dense oxidation → interface activation → nanocomposite sealing".

[0004] In summary, the existing technology has not yet provided a systematic solution to simultaneously and effectively address the three major related problems of TC4 titanium alloy micro-arc oxidation coating: (1) the risk of deep media penetration caused by internal pores and microcracks; (2) the single surface function and lack of stable and wear-resistant hydrophobic protection; and (3) the insufficient reliability of the coating system in long-term service under the dynamic and harsh environment of corrosion and wear coupling.

[0005] Therefore, this invention provides a method for preparing a TC4 titanium alloy micro-arc oxidation composite coating based on laser texture collaboration and its in-situ growth-composite sealing method to solve the following technical problems: (1) how to achieve deep and long-term sealing of the pores and microcracks inside the micro-arc oxidation layer, fundamentally blocking the penetration channels of corrosive media; (2) how to impart stable and wear-resistant hydrophobic properties to the coating surface while sealing the pores, so as to reduce the tendency of media adhesion and erosion; (3) how to improve the bonding strength, wear resistance and corrosion resistance of the coating system simultaneously through process collaborative design, so as to meet the reliability requirements of long-term dynamic service.

[0006] There is an urgent need to develop an innovative composite surface engineering technology that, through precise design and synergistic action in multiple steps, can achieve a deep and durable micro-arc oxide layer while endowing it with stable low surface energy characteristics and enhanced wear resistance, thereby significantly improving the overall service performance and lifespan of TC4 titanium alloy components under real and complex working conditions. Summary of the Invention

[0007] This invention addresses the technical bottlenecks in existing TC4 titanium alloy micro-arc oxidation coatings, such as high porosity leading to a high risk of media penetration, limited surface function and poor hydrophobicity, and weak bonding between the sealing layer and the substrate, resulting in poor wear resistance. In particular, existing solutions are mostly "isolated optimizations," which are difficult to achieve long-term synergistic protection under harsh conditions of coupled corrosion and wear. This invention provides a TC4 titanium alloy micro-arc oxidation composite coating based on laser texture synergy and its in-situ growth-composite sealing method.

[0008] To achieve the above objectives, this invention provides a method for preparing a TC4 titanium alloy micro-arc oxidation composite coating based on laser texture synergy and its in-situ growth-composite sealing process. The core of the preparation method lies in adopting a four-step continuous and synergistic process route of "laser pre-texturing - gradient oxidation film formation - interface hydroxyl activation - nanocomposite sealing". Through the functional complementarity and effect superposition between each step, a surface protection system with dense structure, strong bonding and integrated function is constructed.

[0009] To achieve the above objectives, the technical solution provided by this invention is: an in-situ growth and composite sealing method for a TC4 titanium alloy micro-arc oxidation composite coating based on laser texturing synergy. The preparation method is completed through a four-step process: laser texturing, micro-arc oxidation, hydroxyl activation, and nanocomposite sealing, thereby obtaining the composite coating. Specifically, it includes the following steps: (1) Substrate pretreatment: The TC4 titanium alloy substrate is subjected to gradient mechanical polishing and ultrasonic cleaning in deionized water and ethanol in sequence. After drying, a clean surface is obtained to lay the foundation for subsequent fine processing. (2) Laser-based mesh microtexture construction: The substrate surface treated in step (1) is periodically meshed using an ultrafast picosecond laser to form a micro-rough textured surface with regular concave and convex structures; this step aims to increase the surface area, provide mechanical interlocking points, and guide the uniform growth of the subsequent oxide layer; (3) Gradient voltage micro-arc oxidation: Using the textured surface obtained in step (2) as the anode, micro-arc oxidation is performed in a composite electrolyte containing sodium hexametaphosphate, sodium silicate nonahydrate, sodium citrate and potassium hydroxide using a multi-stage gradually increasing pulse voltage mode. A ceramic oxide layer with TiO2 as the main phase is grown in situ on the textured surface. It is metallurgically bonded to the substrate, and the composite coating is made denser from the inside to the outside due to the voltage gradient control. (4) Surface hydroxylation activation: The micro-arc oxidation sample obtained in step (3) is immersed in an alkaline solution to generate active hydroxyl groups, i.e. -OH, on its surface. Then it is washed and dried. This step is the key chemical bridge connecting the inorganic ceramic layer and the organic sealing layer, providing sufficient bonding sites for the subsequent silanization reaction. (5) Silane / nano silicon nitride composite sealing and curing: Prepare a composite sol with hexadecyltrimethoxysilane (HDTMS) as film-forming agent and nano silicon nitride (Si3N4) as reinforcing phase. Immerse the activated sample in the sol so that the sol can fully penetrate into the pores and microcracks of the micro-arc oxide layer. After hydrolysis and volatilization, heat treatment is performed to cure the sol, thereby forming a composite coating with sealing, hydrophobic and wear-resistant functions on the surface and inside of the micro-arc oxide layer, realizing physical sealing of pores and chemical modification of the surface.

[0010] Preferably, the pulse width of the ultrafast picosecond laser in step (2) is 1-10 picoseconds; the periodic grid in the periodic grid etching is a square grid with a unit size of 50μm×50μm to 400μm×400μm and an etching depth of 5-30μm; this combination of parameters can form a micro-anchoring structure with appropriate scale and uniform distribution while minimizing thermal effects.

[0011] Preferably, the concentrations of each component in the composite electrolyte in step (3) are: sodium hexametaphosphate 10-20 g / L, sodium silicate nonahydrate 5-15 g / L, sodium citrate 10-25 g / L, and potassium hydroxide 3-6 g / L; the multi-stage gradual voltage increase mode is: the voltage starts from 220±10 V, passes through at least 3 intermediate voltage steps, and finally increases to 380±10 V, and each voltage stage includes a slow start period and a constant voltage working period.

[0012] A further preferred formulation contains 15 g / L sodium hexametaphosphate, 10 g / L sodium silicate nonahydrate, 20 g / L sodium citrate, and 4 g / L potassium hydroxide. This formulation exhibits a synergistic effect: sodium hexametaphosphate acts as a complexing stabilizer, sodium silicate promotes glass phase formation and improves density, sodium citrate improves homogeneity, and potassium hydroxide regulates conductivity.

[0013] Preferably, the multi-stage, step-by-step voltage increase consists of six stages: 220V, 250V, 280V, 300V, 350V, and 380V. The pulse frequency of the micro-arc oxidation treatment is 400-600 Hz, and the duty cycle is 8-12%. This "step-by-step" voltage increase mode is beneficial for uniform initial discharge, steady coating thickening in the intermediate stage, and refinement of surface micropores in the final stage, thereby obtaining an oxide layer with optimized structure.

[0014] Preferably, the alkaline solution in step (4) is a sodium hydroxide aqueous solution with a mass fraction of 2-5%, the soaking time of the micro-arc oxidation sample is 10-20 minutes, and the drying temperature is 70-90℃.

[0015] Preferably, the method for preparing the composite sol in step (5) is as follows: first, hexadecyltrimethoxysilane is added to anhydrous ethanol and stirred to form a premix; then, nano-silicon nitride powder is dispersed in an aqueous solution containing a dispersant, and a stable dispersion is obtained by ultrasonic treatment; under stirring conditions, the stable dispersion is added to the premix, and a catalytic amount of deionized water is added, and the mixture is sealed and stirred at room temperature for 6-24 hours to obtain a milky white semi-transparent composite sol; this process ensures the stable dispersion of nanoparticles in the sol and their uniform loading in the final sealing layer.

[0016] Preferably, the particle size of the nano-silicon nitride is 20-100 nm, and the concentration in the composite sol is 0.5-2.0 g / L; the dispersant is a compound of polyacrylamide and polyvinylpyrrolidone.

[0017] Preferably, the heat treatment curing conditions in step (5) are: holding at 120-160℃ for 30-90 minutes, more preferably at 140℃ for 60 minutes. This temperature is sufficient to allow the silane to fully condense and crosslink to form a stable silicon-oxygen network, while avoiding adverse effects on the properties of the titanium alloy matrix.

[0018] The composite coating obtained by the above method in this invention comprises, from the substrate outwards: (1) Laser textured transition zone: located on the surface of the substrate, with a regular micron-scale grid uneven structure.

[0019] (2) Micro-arc oxidation ceramic layer: grown in situ on the textured surface and in the groove, the main phase is TiO2, which is metallurgically bonded to the substrate. This layer itself has a certain hardness and corrosion resistance, but it has inherent micropores and cracks inside.

[0020] (3) Silane / nano-silicon nitride composite sealing layer: This layer not only covers the surface of the ceramic layer, but more importantly, it deeply penetrates and fills the pores and microcracks inside the ceramic layer. It consists of a hydrolyzed and condensed HDTMS silicon-oxygen network as a continuous matrix, in which nano-silicon nitride particles are uniformly embedded. The outward arrangement of long-chain alkyl groups gives the coating hydrophobicity (contact angle >150°), while the nano-silicon nitride acts as a hard reinforcing phase, significantly improving the wear resistance of the surface layer.

[0021] The present invention also discloses a TC4 titanium alloy component, the surface of which has a micro-arc oxidation hydrophobic wear-resistant and corrosion-resistant composite coating obtained by the preparation method described above.

[0022] The present invention also discloses an application of the above-described TC4 titanium alloy component, which is used in structures that are exposed to chloride ion-containing media and accompanied by friction and wear in service environments, including marine engineering equipment, ship components, chemical pumps and valves, and aerospace fasteners.

[0023] Beneficial effects of this invention: 1. Deep sealing and long-term corrosion resistance: Hydroxyl activation enhances the wetting and adhesion of the sealing agent in the pores. Combined with the fluidity of the nanocomposite sol, it achieves deep sealing of the micro-arc oxidation layer from the surface to the interior, greatly extending the path and time for corrosive media to penetrate into the substrate, thus improving the corrosion resistance of the coating by nearly two orders of magnitude.

[0024] 2. Integrated Wear Resistance and Hydrophobicity: The introduction of nano-silicon nitride endows the hydrophobic sealing layer with excellent wear resistance, overcoming the fatal flaw of traditional organic hydrophobic films being poorly wear-resistant. The coating exhibits a lower coefficient of friction and superior durability in tribological tests.

[0025] 3. Strong interfacial bonding and system stability: "Laser texturing" provides mechanical interlocking, while "hydroxyl activation" provides chemical bonding (Si-O-Ti), jointly ensuring a strong and tough bond between the sealing layer and the micro-arc oxidation layer, as well as between the micro-arc oxidation layer and the substrate. This composite coating system exhibits excellent stability under corrosion-wear coupling conditions.

[0026] 4. Process Synergy and Adjustable Performance: The four-step process is interconnected and works synergistically. By adjusting the laser texture parameters, electrolyte composition, voltage program, and sol formulation, the microstructure, hydrophobic angle, wear resistance, and corrosion resistance of the coating can be controlled within a certain range to meet different application requirements. Attached Figure Description

[0027] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention.

[0028] Figure 1 These are SEM comparison photos of the coating surfaces of the four samples from this invention; Figure 2 These are SEM comparison photos of the coating interfaces of the four samples of this invention; Figure 3 This is an EDS diagram showing the elemental distribution and content on the surface of sample No. 5 of this invention; Figure 4 These are the electrochemical Tafel polarization curves of the coatings corresponding to the five samples of this invention; Figure 5 This refers to the coefficient of friction of the coatings corresponding to the five samples of this invention; Figure 6 It is the static contact angle of the coating surface corresponding to the five samples of this invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments and comparative examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless specific conditions are specified, are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all percentages and parts are calculated by weight or volume.

[0030] Example 1: Complete preparation of the composite coating of the present invention This embodiment demonstrates the complete implementation process of the technical solution of the present invention.

[0031] (1) Substrate pretreatment: A TC4 titanium alloy sample measuring 15mm × 15mm × 2mm (composition conforming to GB / T 3620.1 standard) was taken. The six surfaces of the sample were sequentially wet-polished using 400-grit, 800-grit, 1200-grit, and 2000-grit silicon carbide sandpaper. Each time the sandpaper was changed, the sample was rotated 90° to ensure the removal of the previous abrasion marks. After polishing, the sample was placed in glass beakers containing deionized water and analytical grade ethanol, respectively, and cleaned in a 40kHz ultrasonic cleaner for 10 minutes each. After removal, the sample was dried with nitrogen gas and stored in a desiccator for later use.

[0032] (2) Construction of ultrafast laser microtextures: The pretreated sample was fixed on a three-axis precision moving platform of an ultrafast picosecond laser processing system (laser wavelength 1064nm, pulse width 10ps). A square grid was etched onto the upper surface of the sample (a 15mm × 15mm area) using a computer-controlled system. Specific parameters were: laser power 50W, pulse frequency 40kHz, scanning speed 100mm / s, scanning spacing 150μm, single scan. After etching, a regular grid array with a depth of approximately 15μm and a side length of 150μm was formed. The treated sample was rinsed with deionized water and dried with nitrogen.

[0033] (3) Gradient voltage micro-arc oxidation treatment: ① Electrolyte preparation: In a 20L polypropylene tank, add 15L of deionized water preheated to 40℃. Under vigorous stirring (500rpm), slowly add 300g of sodium hexametaphosphate (NaPO3)6 and 400g of sodium citrate (Na3C6H5O7·2H2O) sequentially, stirring until completely dissolved. Then add 200g of sodium silicate nonahydrate (Na2SiO3·9H2O) and continue stirring to dissolve. In a separate beaker, dissolve 80g of potassium hydroxide (KOH) in approximately 1.5L of room temperature deionized water. After cooling, slowly pour the solution into the main tank. Rinse the beaker with a small amount of deionized water and add it to the main tank. Finally, add deionized water to a total volume of 20.0L, stir continuously for 60 minutes, and let stand for later use.

[0034] ② Micro-arc oxidation: The treated sample is used as the anode, and the stainless steel plate surrounding the sample is used as the cathode, immersed in the above-mentioned electrolyte. A bipolar pulse power supply is used for micro-arc oxidation at room temperature. The process parameters are: positive and negative pulse frequencies are both 500Hz, and the duty cycle is 10%. A staged voltage ramping mode is adopted: the initial voltage is 220V (slow start for 5s, operation for 30s), then it is successively increased to 250V, 280V, 300V, and 350V (each stage slow start for 5s, operation for 30s), and finally increased to 380V (slow start for 5s, operation for 210s). During the treatment, air is introduced into the bottom of the electrolyte for stirring at a flow rate of 0.5L / min. After the treatment, the sample is removed, rinsed with deionized water, and dried with nitrogen.

[0035] (4) Surface hydroxylation activation: The micro-arc oxidized sample was completely immersed in a 3% (w / w) sodium hydroxide (NaOH) aqueous solution and allowed to stand for 15 minutes at room temperature (25±2℃). After removal, it was rinsed with plenty of deionized water until neutral and then dried in an 80℃ forced-air drying oven for 15 minutes.

[0036] (5) Silane / nano-silicon nitride composite sealing and curing: ① Preparation of composite sol: a) Solution A (silane premix): In a dry 250 mL Erlenmeyer flask, add 94 mL of anhydrous ethanol and place it on a magnetic stirrer. Using a pipette, measure 3.0 mL of hexadecyltrimethoxysilane (HDTMS) and slowly add it dropwise to the ethanol while stirring. Continue stirring for 15 minutes.

[0037] b) Solution B (nanoparticle dispersion): Weigh 0.10 g of nano-silicon nitride (β-Si3N4, average particle size 50 nm) into a 50 mL centrifuge tube. Add 5.0 mL of pre-prepared dispersant aqueous solution (containing 0.5 wt% polyacrylamide PAM and 0.3 wt% polyvinylpyrrolidone PVP). Place the centrifuge tube in an ultrasonic cell disruptor and ultrasonically disperse at 300 W for 30 minutes to obtain a uniform dispersion.

[0038] c) Mixing and maturation: Under high-speed stirring, solution B was slowly added dropwise to solution A. Then, 1.0 mL of deionized water was accurately added using a pipette. The mixture was sealed and continuously magnetically stirred at room temperature for 8 hours to obtain a stable, milky-white, semi-transparent sol.

[0039] ② Dip Coating and Curing: The hydroxylated and activated sample is vertically clamped using a PTFE clamp and slowly immersed in the sol at a speed of 10 mm / min. After holding for 120 seconds, it is pulled out at the same uniform speed. The sample is placed horizontally in a clean environment and allowed to stand at room temperature for 15 minutes to evaporate. Then, it is transferred to a programmable temperature oven and heated to 140°C at a rate of 5°C / min, and kept at this temperature for 60 minutes. After heat treatment, it is cooled to room temperature in the oven to obtain the composite coating sample described in this invention.

[0040] Example 2: Comparative preparation method omitting laser texturing step This embodiment is used to compare and illustrate the role of the laser texturing step in the synergistic system. Except for omitting step (2) (i.e., directly performing micro-arc oxidation on the polished and cleaned substrate), the preparation process is exactly the same as in Example 1, including the same electrolyte, voltage program, activation, and sealing process.

[0041] Comparative Example 1: Micro-arc oxidation treatment only This comparative example demonstrates a common single micro-arc oxidation coating in the prior art. The micro-arc oxidation coating was prepared according to steps (1) and (3) in Example 1, without laser texturing, hydroxyl activation, and composite sealing treatment.

[0042] Comparative Example 2: After micro-arc oxidation, only conventional silane sealing was performed. This comparative example demonstrates the existing "micro-arc oxidation + single silane sealing" scheme. Based on Example 1, the laser texturing step is omitted, and after micro-arc oxidation, NaOH hydroxylation activation is not performed. Instead, the sol is directly dipped into pure HDTMS silane sol (prepared according to the method of Example 1, but without the addition of nano-Si3N4) without nano-silicon nitride, and the curing conditions are the same.

[0043] Comparative Example 3: Composite sealing material without hydroxylation activation This comparative example illustrates the crucial role of the hydroxylation activation step. Based on Example 1, the micro-arc oxidation sample was not treated with NaOH solution and was directly subjected to composite sol-coating and curing. The remaining steps were identical to those in Example 1.

[0044] Performance Testing and Results Analysis To compare the effects of different process combinations of the present invention on the surface coating structure and performance of TC4 titanium alloy, the samples are numbered as follows: Sample 1 corresponds to TC4 titanium alloy substrate; Sample 2 corresponds to substrate treated with micro-arc oxidation (Comparative Example 1); Sample 3 corresponds to substrate treated with micro-arc oxidation followed by conventional silane sealing (Comparative Example 2); Sample 4 corresponds to micro-arc oxidation followed by hexadecyltrimethoxysilane-modified silicon nitride nanoparticle post-treatment (Example 2); Sample 5 corresponds to picosecond laser texturing + micro-arc oxidation + the above post-treatment (Example 1).

[0045] A series of performance tests were conducted on samples 1-5 above, and the results are summarized below: Coating structure and morphology Figure 1-3 (SEM / EDS) Sample 2 (micro-arc oxidation only) exhibits a typical porous melt morphology with clearly visible pores.

[0046] Sample 3 (conventional silane sealing) has a silane film covering its surface, but the film layer is locally discontinuous, and EDS shows that the nitrogen signal is extremely weak.

[0047] The sealing layer on the surface of sample 4 (without texture) is also relatively uniform, but the cross-section shows that the interface between the sealing layer and the micro-arc oxidation layer is not as dense as that of sample A.

[0048] Sample 5 (of this invention) shows a uniformly covered composite sealing layer on its surface, effectively filling the micropores created by micro-arc oxidation, resulting in a micro-nano composite rough structure. The cross-section reveals that the sealing material penetrates deep into the pores of the coating.

[0049] 2. Corrosion resistance (electrochemical polarization curve test, Figure 4 (3.5wt% NaCl solution): Self-corrosion current density (I) corr ): Sample 5 < Sample 4 < Sample 3 ≈ Sample 2 < Sample 1.

[0050] The results show that sample 5 exhibits the lowest corrosion rate, two orders of magnitude lower than the substrate. Hydroxylation activation (comparison of 5 and 3) and laser texturing (comparison of 5 and 4) both significantly contribute to improved corrosion resistance, with the combination of the two showing the best effect. Conventional silane sealing (sample 3) provides limited long-term protection.

[0051] 3. Wear resistance (ball-disc friction and wear test) Figure 5 ): Average coefficient of friction: Sample 5 < Sample 4 < Sample 3 < Sample 2 < Sample 1.

[0052] Wear track depth and width: The wear track of sample 5 is the shallowest and narrowest, while the silane film of sample 3 is worn through in the early stage of wear.

[0053] The results show that the addition of nano-silicon nitride significantly improves the wear resistance of the sealing layer (compare 5 and 3). Laser texturing may further synergistically improve wear resistance by improving substrate support and stress distribution (compare 5 and 4).

[0054] 4. Hydrophobic properties (static water contact angle measurement) Figure 6 ): Water contact angle: Sample 5 ≈ Sample 4 > Sample 1 > Sample 3 > Sample 2.

[0055] The results show that HDTMS successfully imparted hydrophobicity to the coating. Hydroxylation activation enhanced chemical bonding, making the hydrophobic layer stronger and more uniform, thus achieving a higher and more stable contact angle (compare 5 and 3). The micron-level roughness provided by laser texturing, together with the nanoparticles, constructed a micro / nano secondary structure, further enhancing the hydrophobicity (compare 5 and 2).

[0056] in conclusion: The above examples and comparative examples fully demonstrate that the composite coating (sample 5) successfully prepared by the present invention through a multi-step synergistic process of "ultrafast laser texturing—gradient micro-arc oxidation—hydroxylation activation—silane / nano-silicon nitride composite sealing" exhibits superior comprehensive performance in terms of corrosion resistance, wear resistance, and hydrophobicity, significantly outperforming any single process or simple combination process (samples 1-4). This verifies the effectiveness and innovation of the present invention in solving the problems described in the background art.

[0057] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for in-situ growth and composite sealing of a TC4 titanium alloy micro-arc oxidation composite coating based on laser texture synergy, characterized in that: The preparation method is completed through a four-step process of laser texturing, micro-arc oxidation, hydroxyl activation, and nanocomposite sealing, thereby obtaining a composite coating. Specifically, it includes the following steps: (1) Substrate pretreatment: The TC4 titanium alloy substrate was subjected to gradient mechanical polishing and ultrasonic cleaning in deionized water and ethanol in sequence. After drying, a clean surface was obtained. (2) Laser-based mesh microtexture construction: The substrate surface after step (1) is periodically etched with an ultrafast picosecond laser to form a micro-rough textured surface with a regular concave-convex structure; (3) Gradient voltage micro-arc oxidation: Using the textured surface obtained in step (2) as the anode, micro-arc oxidation is performed in a composite electrolyte containing sodium hexametaphosphate, sodium silicate nonahydrate, sodium citrate and potassium hydroxide using a multi-stage gradually increasing pulse voltage mode, and a ceramic oxide layer with TiO2 as the main phase is grown in situ on the textured surface. (4) Surface hydroxylation activation: The micro-arc oxidation sample obtained in step (3) is immersed in an alkaline solution to generate active hydroxyl groups, i.e. -OH, on its surface, and then washed and dried. (5) Silane / nano silicon nitride composite sealing and curing: Prepare a composite sol with hexadecyltrimethoxysilane as film-forming agent and nano silicon nitride as reinforcing phase. Immerse the activated sample in the sol so that the sol can fully penetrate into the pores and microcracks of the micro-arc oxidation layer. After hydrolysis and volatilization, heat treatment is performed to cure, thereby forming a composite coating with sealing, hydrophobic and wear-resistant functions on the surface and inside of the micro-arc oxidation layer.

2. The preparation method according to claim 1, characterized in that: The pulse width of the ultrafast picosecond laser in step (2) is 1-10 picoseconds; the periodic grid in the periodic grid etching is a square grid with a unit size of 50μm×50μm to 400μm×400μm and an etching depth of 5-30μm.

3. The preparation method according to claim 1, characterized in that: In step (3), the concentrations of each component in the composite electrolyte are: sodium hexametaphosphate 10-20 g / L, sodium silicate nonahydrate 5-15 g / L, sodium citrate 10-25 g / L, and potassium hydroxide 3-6 g / L. The multi-stage gradual voltage increase mode is as follows: the voltage starts from 220±10 V, passes through at least 3 intermediate voltage steps, and finally increases to 380±10 V. Each voltage stage includes a slow start period and a constant voltage working period.

4. The preparation method according to claim 3, characterized in that: The multi-stage, progressively increasing voltage consists of six stages: 220V, 250V, 280V, 300V, 350V, and 380V. The pulse frequency of the micro-arc oxidation treatment is 400-600Hz, and the duty cycle is 8-12%.

5. The preparation method according to claim 1, characterized in that: The alkaline solution in step (4) is a sodium hydroxide aqueous solution with a mass fraction of 2-5%, and the soaking time of the micro-arc oxidation sample is 10-20 minutes; the drying temperature is 70-90℃.

6. The preparation method according to claim 1, characterized in that: The method for preparing the composite sol in step (5) is as follows: first, add hexadecyltrimethoxysilane to anhydrous ethanol and stir to form a premix; then, disperse nano-silicon nitride powder in an aqueous solution containing a dispersant, and obtain a stable dispersion by ultrasonic treatment; under stirring conditions, add the stable dispersion to the premix, add a catalytic amount of deionized water, and seal and stir at room temperature for 6-24 hours to obtain a milky white semi-transparent composite sol.

7. The preparation method according to claim 1, characterized in that: The nano-silicon nitride has a particle size of 20-100 nm and a concentration of 0.5-2.0 g / L in the composite sol; the dispersant is a compound of polyacrylamide and polyvinylpyrrolidone.

8. The preparation method according to claim 1, characterized in that: The heat treatment curing conditions in step (5) are: heat treatment at 120-160℃ for 30-90 minutes.

9. A TC4 titanium alloy component, characterized in that: The surface of the TC4 titanium alloy component has a micro-arc oxidation hydrophobic wear-resistant and corrosion-resistant composite coating obtained by the preparation method described in any one of claims 1-8.

10. An application of a TC4 titanium alloy component according to claim 9, characterized in that: TC4 titanium alloy components are used in structures that are exposed to chloride-containing media and frictional wear for extended periods, including marine engineering equipment, ship components, chemical pumps and valves, and aerospace fasteners.

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