Preparation process of nano-particle composite micro-arc oxidation coating suitable for near-beta type titanium alloy

Abstract

The invention relates to the field of titanium alloy surface treatment, in particular to a preparation process of a nano-particle composite micro-arc oxidation coating suitable for a near-beta type titanium alloy. The preparation process comprises the following steps: step 1, degreasing treatment; step 2, membrane removal treatment; 3, performing nano-particle doping arc oxidation treatment to obtain a hard micro-arc oxidation film; and 4, PTFE paint film spraying treatment is conducted, and the PTFE paint film is obtained. The nano-particle composite micro-arc oxidation coating is of a double-layer structure, after nano-particle doped arc oxidation treatment, an inner-layer wear-resistant hard micro-arc oxidation film with the thickness being 20-30 microns and the average microhardness being 850 HV or above can be prepared on the near-beta-type titanium alloy, wear resistance and sufficient bearing capacity are provided for the composite coating, and by combining with an outer-layer PTFE paint film, the wear resistance of the composite coating is greatly improved. The near-beta type titanium alloy can be endowed with antifriction and wear-resistant double characteristics, a long-acting and lasting wear-resistant effect is provided, and the problem that the surface of a high-proportion beta phase in a matrix is not prone to oxidation is effectively solved.

Description

Technical Field

[0001] The invention relates to the field of titanium alloy surface treatment, in particular to a process for preparing a nano-particle composite micro-arc oxidation coating suitable for near-β titanium alloys. Background Art

[0002] Micro-arc oxidation (MAO) offers advantages such as low cost, low pollution, and high automation, making it a commonly used surface treatment technique for improving the wear resistance of titanium alloys. However, the quality of the films produced by MAO treatment is poor for certain titanium alloy grades. Near-β titanium alloys, such as TB2, TB3, TB5, TB6, TB8, TB9, TB10, BT30, and TC18, contain β-stabilizing elements slightly above the critical concentration (the minimum concentration required to retain the high-temperature β phase at room temperature during rapid cooling). These near-β titanium alloys exhibit high strength and toughness and are widely used in aircraft structural components. Due to the heterogeneous matrix microstructure of these titanium alloys, with the β phase accounting for 40% to 70% of the surface area, MAO films are difficult to deposit uniformly on these surfaces, as the β phase is rich in alloying elements such as V and Mo that are difficult to oxidize, severely impacting film quality. For engineering applications, the development of high-performance MAO coatings suitable for near-β titanium alloys is urgently needed. Summary of the Invention

[0003] The purpose of the present invention is to provide a process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloys, which effectively solves the problem that the surface of the β phase with a high proportion in the near-β titanium alloy matrix is ​​not easily oxidized.

[0004] The technical solution of the present invention is:

[0005] A process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloys, the specific steps are as follows:

[0006] Step 1: Degreasing

[0007] Immerse the titanium alloy workpiece to be treated in a degreasing treatment liquid at 80℃~90℃, and control the treatment time within the range of 3min~10min according to the surface condition of the workpiece to remove grease and dirt attached to the surface of the workpiece;

[0008] Step 2: Film removal

[0009] The degreased titanium alloy is immersed in a film removal treatment solution at room temperature for 10 seconds to 5 minutes to remove the surface oxide scale and initial passivation film generated by machining, thereby obtaining a uniform surface state;

[0010] Step 3: Nanoparticle doping arc oxidation treatment

[0011] The titanium alloy after film removal was electrically connected using a fixture made of the same material and placed in a composite electrolyte doped with high-hardness nanoparticles for constant current-constant voltage staged micro-arc oxidation treatment to obtain a hard micro-arc oxidation film.

[0012] Step 4: PTFE paint spraying

[0013] The titanium alloy after micro-arc oxidation treatment is sprayed with commercial PTFE Teflon coating to obtain a PTFE paint film.

[0014] The nanoparticle composite micro-arc oxidation coating preparation process suitable for near-β titanium alloys, in step 1, the degreasing treatment liquid uses a commercial metal cleaning agent or an alkaline solution; the alkaline solution uses a single or compound aqueous solution of sodium hydroxide, sodium carbonate, and sodium bicarbonate, and the concentrations of sodium hydroxide, sodium carbonate, and sodium bicarbonate are 20-60g / l, 0g / l-60g / l, and 0g / l-30g / l, respectively, and the balance is water.

[0015] The nanoparticle composite micro-arc oxidation coating preparation process suitable for near-β titanium alloy, in step 2, the film removal treatment liquid contains nitric acid, hydrofluoric acid, and an organic amine corrosion inhibitor, and the contents of nitric acid, hydrofluoric acid, and organic amine corrosion inhibitor are 60ml / l~150ml / l, 40ml / l~100ml / l, and 20g / l~80g / l, respectively, and the balance is water.

[0016] The nanoparticle composite micro-arc oxidation coating preparation process suitable for near-β titanium alloys is characterized in that in step 3, the constant current-constant voltage stage micro-arc oxidation treatment process is carried out in the first step of oxidation at 10A / dm -2 ~15A / dm -2 The constant current density is oxidized to above 350V, and the second step adopts the constant voltage mode to continue oxidation for 5min to 60min.

[0017] In the process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloy, in step 3 of the constant current-constant voltage staged micro-arc oxidation treatment process, the electrical parameters of the second step are set to a constant voltage of 350V to 480V, a positive duty cycle of 20% to 50%, and a frequency of 100Hz to 1500Hz; during the micro-arc oxidation process, water cooling or air cooling is used to control the electrolyte temperature within the range of 20°C to 50°C, and an air compressor is used for aeration to ensure uniform temperature at various locations in the electrolyte.

[0018] The process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloys comprises: in step 3, the high-hardness nanoparticle-doped composite electrolyte comprising 6 g / L to 12 g / L of silicate, 0.5 g / L to 5 g / L of aluminate, 5 g / L to 12 g / L of phosphate, 1 g / L to 2 g / L of sodium hydroxide, 0.5 g / L to 3 g / L of complexing agent, 0.5 g / L to 2 g / L of dispersant, 0.5 g / L to 3 g / L of modified high-hardness nanoparticles, and the balance being water; during the preparation of the composite electrolyte, various chemical reagents need to be completely dissolved in deionized water and then fully mixed, and finally the modified high-hardness nanoparticles are added, and magnetic stirring is adopted for more than 30 minutes.

[0019] The nanoparticle composite micro-arc oxidation coating preparation process suitable for near-β titanium alloys is as follows: in the composite electrolyte doped with high-hardness nanoparticles in step 3, the silicate is a combination of one or more of sodium silicate, sodium fluorosilicate, and aluminum silicate, the aluminate is a combination of one or more of sodium aluminate, sodium metaaluminate, and calcium aluminate, and the phosphate is a combination of one or more of sodium hexametaphosphate, sodium polyphosphate, and trisodium phosphate; the high-hardness nanoparticles are Al2O3 or SiO2, and the size is 50nm to 200nm.

[0020] In the process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloys, in the composite electrolyte doped with high-hardness nanoparticles in step 3, the high-hardness nanoparticles are chemically modified before use using a 0.5ml / l to 2ml / l aqueous solution of triethanolamine, acetylene glycol, or acetylene glycol polyvinyl ether, or a combination of two or more, and mechanically stirred at a speed of 100r / min to 300r / min for more than 30 minutes using a ball mill.

[0021] In the process for preparing the nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloy, in step 4, during the commercial PTFE Teflon coating spraying process, the PTFE paint film thickness is controlled at 20 μm to 50 μm, and the sprayed nanoparticle composite micro-arc oxidation coating is cured at 280° C. for 10 minutes.

[0022] The nanoparticle composite micro-arc oxidation coating preparation process suitable for near-β titanium alloy has a double-layer structure. After the nanoparticle doped arc oxidation treatment, an inner wear-resistant hard micro-arc oxidation film with a thickness of 20μm to 30μm and an average microhardness of 850HV or above can be prepared on the near-β titanium alloy. Combined with the outer PTFE paint film, it can give the near-β titanium alloy the dual properties of friction reduction and wear resistance, providing a long-lasting anti-wear effect.

[0023] The design concept of the present invention is:

[0024] To achieve optimal wear resistance for near-β titanium alloys, the present invention proposes a composite treatment scheme combining a hard micro-arc oxide film and a lubricating paint film, resulting in a composite coating that combines both friction reduction and wear resistance. The high-hardness micro-arc oxide film serves as the base layer, primarily providing excellent wear resistance and load-bearing capacity for the composite coating, ensuring structural stability under high-load wear conditions. The outer layer of the oxide film is coated with a PTFE-doped organic paint film. The low-shear stress PTFE acts as a lubricant during wear, isolating the friction surfaces to reduce friction.

[0025] Among them, how to prepare a high-hardness micro-arc oxidation film on the surface of near-β titanium alloy is a difficulty in composite coating. The main reason for the difficulty in forming a high-quality micro-arc oxidation film on the surface of near-β titanium alloy is that the substrate has a high proportion of β phase structure, resulting in uneven deposition of the initial oxide film. To address this problem, the present invention has designed the following three solutions:

[0026] 1) Pretreatment: Improve the surface condition of the substrate before micro-arc oxidation treatment as much as possible, remove the surface oxide scale and passivation film, and improve the surface uniformity; 2) Electrolyte: Add film-forming substances with high adsorption energy or high deposition rate to increase the deposition rate of external oxides from the electrolyte, make up for the defect of difficult film formation on the β-phase surface, and improve the microporous state of the oxide film; 3) Oxidation electrical parameters: In the early stage of oxidation, promote the formation of the initial oxide film, achieve uniform coverage of the film-forming substance in a short time, and in the later stage of oxidation, continue to thicken and suppress arc discharge.

[0027] In view of the above three solutions, the present invention makes the following improvements:

[0028] 1) Pretreatment: The present invention first develops a descaling process suitable for near-β-type titanium alloys, which completely removes the machine-added oxide scale and passivation film formed on the surface of the substrate, improves the surface state of the substrate and increases its surface activity; 2) Electrolyte: Through chemical modification, high-hardness nanoparticles are made negatively charged and evenly dispersed in the electrolyte, and migrate to the surface of the anode workpiece under the action of the electric field, assisting film formation by doping and adsorption. In addition, the doping of nanoparticles can improve the micropore structure on the surface of the micro-arc oxidation film, which is beneficial to the subsequent filling of the lubricating paint film, improves the bonding strength of the paint film and realizes the gradual release of lubricating components during the wear process; 3) Oxidation electrical parameters: The constant current with high current density in the first step is conducive to the rapid formation of the initial oxide film, reducing the influence of the microstructure on the oxidation process. The constant voltage mode in the second step effectively suppresses the local violent arc discharge in the later stage of micro-arc oxidation, and realizes the stable and uniform thickening of the film layer. The three factors work together to achieve high-quality oxidation film formation of titanium alloys with a high β phase ratio.

[0029] The present invention has the following advantages and beneficial effects:

[0030] 1. This invention optimizes the design from three aspects: pretreatment (descaling process), electrolyte formulation (nanoparticle modification), and oxidation parameters (constant current-constant voltage staged oxidation). This reduces the influence of the titanium alloy substrate microstructure on initial film formation and addresses the problem of poor film quality of micro-arc oxidation films on near-β titanium alloys. The micro-arc oxidation composite coating has a two-layer structure. After oxidation in an electrolyte doped with modified nanoparticles, the inner hard micro-arc oxidation film has a thickness of 20 to 30 μm and an average microhardness of over 850 HV, providing the composite coating with wear resistance and sufficient load-bearing capacity.

[0031] 2. The inner high-hardness micro-arc oxidation film of the present invention is combined with the lubricating effect of the outer PTFE Teflon paint film, so that the composite coating has both friction reduction and wear resistance properties, providing a long-lasting and durable anti-wear effect for the near-β titanium alloy substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1-Figure 2 .Macromorphology of micro-arc oxidation film on near-β titanium alloy. Figure 1 Traditional micro-arc oxidation film; Figure 2 Example 1 Nanoparticle-doped micro-arc oxidation film.

[0033] Figure 3-Figure 4 .Morphology of near-β-type titanium alloy nanoparticle composite micro-arc oxidation coating. Among them, Figure 3 Surface morphology of nanoparticle-doped micro-arc oxidation film in Example 1; Figure 4 Cross-sectional morphology of the double-layer composite membrane of Example 1. DETAILED DESCRIPTION

[0034] In the specific implementation process, the preparation process of the nanoparticle composite micro-arc oxidation coating of the near-β titanium alloy of the present invention is mainly divided into the following three steps:

[0035] Step 1: Degreasing: Soak in a commercial metal cleaning agent or alkaline solution at 80℃ to 90℃ for 3min to 10min to remove grease and dirt on the surface of the workpiece;

[0036] In the alkaline solution, the concentrations of sodium hydroxide, sodium carbonate, and sodium bicarbonate are 20-60 g / l, 0 g / l-60 g / l, and 0 g / l-30 g / l, respectively, with the balance being water;

[0037] Step 2: Film removal treatment: Soak the degreased titanium alloy in a film removal treatment solution at room temperature for 10 seconds to 5 minutes to remove the surface oxide scale and initial passivation film generated by machining, thereby obtaining a uniform surface state.

[0038] In the film removal treatment solution, the concentrations of nitric acid, hydrofluoric acid, and organic amine corrosion inhibitor are 60ml / l to 150ml / l, 40ml / l to 100ml / l, and 20g / l to 80g / l, respectively, and the balance is water;

[0039] Steps 1 and 2 are pretreatments, mainly used to remove oil stains and oxide scale attached to the surface of the titanium alloy and improve the surface uniformity of the substrate before oxidation treatment.

[0040] Step 3: Nano-doped micro-arc oxidation treatment

[0041] The titanium alloy after the film removal treatment was electrically connected with the same material fixture and placed in a composite electrolyte doped with high hardness nanoparticles for constant current-constant voltage staged micro-arc oxidation treatment: first, the titanium alloy was heated at 10A / dm -2 ~15A / dm -2 The micro-arc oxidation process is carried out at a constant current density of 350V or above, and then switched to constant voltage mode for further oxidation for 5 to 60 minutes. In constant voltage mode, the electrical parameters include a constant voltage of 350V to 480V, a positive duty cycle of 20% to 50%, and a frequency of 100Hz to 1500Hz. During the micro-arc oxidation process, flowing water cooling and air pump aeration are used to reduce the electrolyte temperature and ensure uniform temperature distribution in the tank.

[0042] The composite electrolyte contains 6g / L to 12g / L of silicate, 0.5g / L to 5g / L of aluminate, 5g / L to 12g / L of phosphate, 1g / L to 2g / L of sodium hydroxide, 0.5g / L to 3g / L of a complexing agent, 0.5g / L to 2g / L of a dispersant, and 0.5g / L to 3g / L of modified high-hardness nanoparticles, with the balance being water. During the preparation of the composite electrolyte, each chemical reagent must be completely dissolved in deionized water and then thoroughly mixed. Finally, the modified high-hardness nanoparticles are added and magnetic stirring is applied for at least 30 minutes. Among them, high-hardness nanoparticles need to be chemically modified with a single or compound aqueous solution of 0.5ml / l to 2ml / l triethanolamine, acetylene glycol, or acetylene glycol polyvinyl ether before use, and mechanically stirred at a speed of 100r / min to 300r / min for more than 30 minutes using a ball mill. The effect of modifying high-hardness nanoparticles is: on the one hand, to increase the hard phase content on the surface of the micro-arc oxidation film and improve the surface hardness; on the other hand, to assist film formation, increase the film thickness, and improve the bearing capacity.

[0043] Step 4: PTFE paint spraying

[0044] The surface of the high-hardness micro-arc oxidation film obtained in step 3 is sprayed with commercial PTFE Teflon coating to provide lubricity. The thickness of the PTFE coating is controlled at 20 μm to 50 μm. The sprayed PTFE coating is cured at a high temperature of 280° C. for 10 minutes.

[0045] The technical solution of the present invention is further described in detail below through examples and drawings.

[0046] Example 1

[0047] In this embodiment, the sample is TC18 titanium alloy plate, and the specific steps are as follows:

[0048] (1) Degreasing treatment: The titanium alloy plate was immersed in an alkaline solution at 80°C for 10 min. The alkaline solution consisted of 30 g / l sodium hydroxide, 30 g / l sodium carbonate, 30 g / l sodium bicarbonate, and the balance was water.

[0049] (2) Film removal treatment: After degreasing, the titanium alloy plate is washed with water and then immersed in a film removal treatment solution for 2 minutes at room temperature. The film removal treatment solution is 60 ml / l of nitric acid, 80 ml / l of hydrofluoric acid, 20 g / l of an organic amine corrosion inhibitor (such as diethylamine), and the balance is water;

[0050] (3) Nanoparticle doping micro-arc oxidation treatment: The titanium alloy plate after film removal treatment is washed with water and then placed in a micro-arc oxidation electrolyte for micro-arc oxidation treatment. The micro-arc oxidation electrolyte includes 6g / l sodium fluorosilicate, 6g / l sodium silicate, 0.5g / l sodium aluminate, 6g / l sodium hexametaphosphate, 2g / l sodium hydroxide, 0.5g / l complexing agent (such as sodium gluconate), 0.5g / l Al2O3 nanoparticles, 0.5g / l dispersant (such as sodium dodecylbenzenesulfonate), and the balance is water; wherein, the Al2O3 nanoparticles (particle size of 50nm to 100nm) are chemically modified with a 0.5ml / l triethanolamine aqueous solution before addition, and mechanically stirred at 100r / min for 30min using a ball mill.

[0051] The first step of oxidation was carried out at a constant current of 10A / dm -2 Oxidation to 350V, the second step constant voltage 480V, positive duty cycle 20%, frequency 200Hz oxidation treatment for 20min, flowing water cooling and air aeration during the oxidation process, can prepare a hard micro-arc oxidation film with a thickness of 21μm on the titanium alloy plate.

[0052] (4) PTFE paint film spraying treatment

[0053] Commercial PTFE Teflon coating was used for spraying, and the thickness of the PTFE paint film was controlled at 50 μm. The sprayed titanium alloy plate was cured at a high temperature of 280°C for 10 minutes.

[0054] Example 2

[0055] In this embodiment, the sample is a BT30 titanium alloy plate, and the specific steps are as follows:

[0056] (1) Degreasing treatment: The titanium alloy plate was immersed in an alkaline solution at 80°C for 5 min. The alkaline solution consisted of 30 g / l sodium hydroxide, 30 g / l sodium carbonate, 30 g / l sodium bicarbonate, and the balance was water.

[0057] (2) Film removal treatment: After degreasing, the titanium alloy plate is washed with water and then immersed in a film removal treatment solution for 30 seconds at room temperature. The film removal treatment solution is 80 ml / l of nitric acid, 120 ml / l of hydrofluoric acid, 60 g / l of an organic amine corrosion inhibitor (such as diethylamine), and the balance is water;

[0058] (3) Nanoparticle doping micro-arc oxidation treatment: After the film removal treatment, the titanium alloy plate is washed with water and placed in a micro-arc oxidation electrolyte for micro-arc oxidation treatment. The micro-arc oxidation electrolyte includes 8g / l sodium fluorosilicate, 2g / l aluminum silicate, 2g / l sodium aluminate, 1g / l sodium metaaluminate, 2g / l trisodium phosphate, 4g / l sodium hexametaphosphate, 2g / l sodium hydroxide, 1g / l complexing agent (such as disodium ethylenediaminetetraacetic acid), 1g / l SiO2 nanoparticles, 1g / l dispersant (such as oleyl amino oleate), and the balance is water. Among them, the SiO2 nanoparticles (particle size of 50nm to 100nm) are chemically modified with 1ml / l acetylene glycol aqueous solution before addition and mechanically stirred at 200r / min using a ball mill for 30min.

[0059] The first step of oxidation was carried out at a constant current of 12A / dm -2 Oxidation to 350V, the second step constant voltage 450V, positive duty cycle 30%, frequency 600Hz oxidation treatment for 10min, flowing water cooling and air aeration during the oxidation process, can prepare a hard micro-arc oxidation film with a thickness of 20μm on the titanium alloy plate.

[0060] (4) PTFE paint film spraying treatment

[0061] Commercial PTFE Teflon coating was used for spraying, and the thickness of the PTFE paint film was controlled at 30 μm. The sprayed titanium alloy plate was cured at a high temperature of 280°C for 10 minutes.

[0062] Example 3

[0063] In this embodiment, the sample is TC18 titanium alloy plate, and the specific steps are as follows:

[0064] (1) Degreasing treatment: The titanium alloy plate was immersed in an alkaline solution at 80°C for 5 min. The alkaline solution consisted of 30 g / l sodium hydroxide, 30 g / l sodium carbonate, 30 g / l sodium bicarbonate, and the balance was water.

[0065] (2) Film removal treatment: After degreasing, the titanium alloy plate is washed with water and then immersed in a film removal treatment solution for 2 minutes at room temperature. The film removal treatment solution is 100 ml / l of nitric acid, 120 ml / l of hydrofluoric acid, 80 g / l of an organic amine corrosion inhibitor (such as diethylamine), and the balance is water;

[0066] (3) Nanoparticle doping micro-arc oxidation treatment: After the film removal treatment, the titanium alloy plate is washed with water and placed in a micro-arc oxidation electrolyte for micro-arc oxidation treatment. The micro-arc oxidation electrolyte includes 6g / l sodium silicate, 2g / l sodium fluorosilicate, 3g / l sodium aluminate, 3g / l trisodium phosphate, 2g / l sodium polyphosphate, 1g / l sodium hydroxide, 2g / l complexing agent (such as tartaric acid), 2g / l Al2O3 nanoparticles, 1.5g / l dispersant (such as polyethylene glycol), and the balance is water. Among them, the Al2O3 nanoparticles (particle size of 50nm to 100nm) are chemically modified with a 1.5ml / l triethanolamine aqueous solution before addition and mechanically stirred at 100r / min using a ball mill for 30min.

[0067] The first step of oxidation was carried out at a constant current of 12A / dm -2 Oxidation to 380V, the second step constant voltage 480V, positive duty cycle 50%, frequency 1000Hz oxidation treatment for 30min, flowing water cooling and air aeration during the oxidation process, can prepare a hard micro-arc oxidation film with a thickness of 22μm on the titanium alloy plate.

[0068] (4) PTFE paint film spraying treatment

[0069] Commercial PTFE Teflon coating was used for spraying, and the thickness of the PTFE paint film was controlled at 35 μm. The sprayed titanium alloy plate was cured at a high temperature of 280°C for 10 minutes.

[0070] Example 4

[0071] In this embodiment, the sample is a BT30 titanium alloy plate, and the specific steps are as follows:

[0072] (1) Degreasing treatment: Soak the titanium alloy plate in an alkaline solution at 85°C for 10 min. The alkaline solution consists of 30 g / l sodium hydroxide, 30 g / l sodium carbonate, 30 g / l sodium bicarbonate, and the balance water.

[0073] (2) Film removal treatment: After degreasing, the titanium alloy plate is washed with water and then immersed in a film removal treatment solution for 30 seconds at room temperature. The film removal treatment solution is 80 ml / l of nitric acid, 80 ml / l of hydrofluoric acid, 50 g / l of an organic amine corrosion inhibitor (such as diethylamine), and the balance is water;

[0074] (3) Nanoparticle doping micro-arc oxidation treatment: After the film is removed, the titanium alloy plate is washed with water and placed in a micro-arc oxidation electrolyte for micro-arc oxidation treatment. The micro-arc oxidation electrolyte includes 4g / l aluminum silicate, 4g / l sodium fluorosilicate, 2g / l calcium aluminate, 1g / l sodium aluminate, 6g / l trisodium phosphate, 2g / l sodium polyphosphate, 1g / l sodium hydroxide, 2g / l complexing agent (such as sodium gluconate), 3g / l SiO2 nanoparticles, 0.5g / l dispersant (such as sodium dodecylbenzenesulfonate), and the balance is water. Among them, the SiO2 nanoparticles (particle size of 50nm to 100nm) are chemically modified with 1ml / l aqueous solution of acetylene glycol before addition and mechanically stirred at 150r / min using a ball mill for 30min.

[0075] The first step of oxidation was carried out at a constant current of 15A / dm -2 Oxidation to 360V, the second step constant voltage 450V, positive duty cycle 50%, frequency 800Hz oxidation treatment for 50min, flowing water cooling and air aeration during the oxidation process, can prepare a hard micro-arc oxidation film with a thickness of 23μm on the titanium alloy plate.

[0076] (4) PTFE paint film spraying treatment

[0077] Commercial PTFE Teflon coating was used for spraying, and the thickness of the PTFE paint film was controlled at 35 μm. The sprayed titanium alloy plate was cured at a high temperature of 280°C for 10 minutes.

[0078] like Figure 1-Figure 4 As shown in Figure 1, the titanium alloy plate subjected to micro-arc oxidation composite treatment in Example 1 was characterized in terms of macro- and micro-morphology. The results show that although the surface area of ​​the β phase in the TC18 titanium alloy matrix to be oxidized accounts for 59%, which is higher than that of the α phase, a uniform, complete, light brown micro-arc oxidation film can still be formed on its surface after the nano-doped micro-arc oxidation treatment of the present invention. The average thickness of the film layer is about 23 μm. Microhardness tests (load 500N) were performed on 6 randomly selected positions on the surface, and the test results were 758HV, 858HV, 1041HV, 732HV, 834HV, and 898HV, respectively, with an average microhardness of 853HV. In addition, the reasonable microporous structure is compatible with the PTFE paint film, and there is good interface bonding between the micro-arc oxidation film and the PTFE paint film.

Claims

1. A process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloy, characterized in that: The specific steps are as follows: Step 1: Degreasing Immerse the titanium alloy workpiece to be treated in a degreasing treatment liquid at 80℃~90℃, and control the treatment time within the range of 3min~10min according to the surface condition of the workpiece to remove grease and dirt attached to the surface of the workpiece; Step 2: Film removal The degreased titanium alloy is immersed in a film removal treatment solution at room temperature for 10 seconds to 5 minutes to remove the surface oxide scale and initial passivation film generated by machining, thereby obtaining a uniform surface state; Step 3: Nanoparticle doping arc oxidation treatment The titanium alloy after film removal was electrically connected using a fixture made of the same material and placed in a composite electrolyte doped with high-hardness nanoparticles for constant current-constant voltage staged micro-arc oxidation treatment to obtain a hard micro-arc oxidation film. Step 4: PTFE paint spraying The titanium alloy after micro-arc oxidation treatment is sprayed with commercial PTFE Teflon coating to obtain a PTFE paint film.

2. The process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloy according to claim 1, characterized in that: In step 1, the degreasing treatment liquid uses a commercial metal cleaning agent or an alkaline solution; the alkaline solution uses a single or compound aqueous solution of sodium hydroxide, sodium carbonate, and sodium bicarbonate, with the concentrations of sodium hydroxide, sodium carbonate, and sodium bicarbonate being 20-60 g / l, 0 g / l-60 g / l, and 0 g / l-30 g / l, respectively, and the balance being water.

3. The process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloy according to claim 1, characterized in that: In step 2, the film removal treatment solution contains nitric acid, hydrofluoric acid, and an organic amine corrosion inhibitor. The contents of nitric acid, hydrofluoric acid, and the organic amine corrosion inhibitor are 60 ml / l to 150 ml / l, 40 ml / l to 100 ml / l, and 20 g / l to 80 g / l, respectively, and the balance is water.

4. The process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloy according to claim 1, characterized in that: In step 3, the constant current-constant voltage stage micro-arc oxidation process, the first oxidation step is 10A / dm -2 ~15A / dm -2 The constant current density is oxidized to above 350V, and the second step adopts the constant voltage mode to continue oxidation for 5min to 60min.

5. The process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloy according to claim 4, characterized in that: In step 3 of the constant current-constant voltage staged micro-arc oxidation treatment process, the second-step electrical parameters are set to a constant voltage of 350V to 480V, a positive duty cycle of 20% to 50%, and a frequency of 100Hz to 1500Hz. During the micro-arc oxidation process, water cooling or air cooling is used to control the electrolyte temperature within the range of 20°C to 50°C, and an air compressor is used for aeration to ensure uniform temperature at all locations in the electrolyte.

6. The process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloy according to claim 1, characterized in that: In step 3, the composite electrolyte doped with high-hardness nanoparticles includes 6g / L~12g / L of silicate, 0.5g / L~5g / L of aluminate, 5g / L~12g / L of phosphate, 1g / L~2g / L of sodium hydroxide, 0.5g / L~3g / L of complexing agent, 0.5g / L~2g / L of dispersant, 0.5g / L~3g / L of modified high-hardness nanoparticles, and the balance is water; during the preparation of the composite electrolyte, various chemical reagents need to be completely dissolved in deionized water and then fully mixed, and finally the modified high-hardness nanoparticles are added, and magnetic stirring is used for more than 30 minutes.

7. The process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloy according to claim 6, characterized in that: In the composite electrolyte doped with high-hardness nanoparticles in step 3, the silicate is a combination of one or more of sodium silicate, sodium fluorosilicate, and aluminum silicate, the aluminate is a combination of one or more of sodium aluminate, sodium metaaluminate, and calcium aluminate, and the phosphate is a combination of one or more of sodium hexametaphosphate, sodium polyphosphate, and trisodium phosphate; the high-hardness nanoparticles are Al2O3 or SiO2, and the size is 50nm to 200nm.

8. The process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloy according to claim 6, characterized in that: In the composite electrolyte doped with high-hardness nanoparticles in step 3, the high-hardness nanoparticles must be chemically modified with a 0.5 ml / l to 2 ml / l aqueous solution of triethanolamine, acetylene glycol, or acetylene glycol polyvinyl ether, or a combination of two or more, before use, and mechanically stirred at a speed of 100 r / min to 300 r / min for more than 30 minutes using a ball mill.

9. The process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloy according to claim 1, characterized in that: In step 4, in the commercial PTFE Teflon coating spraying process, the PTFE paint film thickness is controlled at 20 μm to 50 μm, and the sprayed nanoparticle composite micro-arc oxidation coating is cured at 280° C. for 10 minutes.

10. The process for preparing a nanoparticle composite micro-arc oxidation coating suitable for near-β titanium alloy according to any one of claims 1 to 9, characterized in that: The nanoparticle composite micro-arc oxidation coating has a double-layer structure. After the nanoparticle doped arc oxidation treatment, an inner wear-resistant hard micro-arc oxidation film with a thickness of 20μm to 30μm and an average microhardness of more than 850HV can be prepared on the near-β titanium alloy. Combined with the outer PTFE paint film, it can give the near-β titanium alloy the dual properties of friction reduction and wear resistance, providing a long-lasting anti-wear effect.

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