Preparation method and application of wear-resistant composite gradient film layer on surface of titanium alloy

Abstract

The invention belongs to the technical field of surface modification, and particularly relates to a preparation method and application of a titanium alloy surface wear-resistant composite gradient film layer. The titanium alloy composite gradient film prepared through the method has high compactness and thickness and shows an obvious evolution rule, and when the zirconium sulfate solution is dropwise added into the electrolyte for 13-17 min, the surface of the film is smooth, pores are fine and uniform, and the thickness is appropriate; when the dropwise adding time of the zirconium sulfate solution is less than 13 minutes, pores of the film layer are increased and non-uniform, and the concentration of zirconium sulfate is relatively low, so that the growth of the film layer is inhibited, and the thickness is small; when the dropwise adding time of the zirconium sulfate solution is longer than 17 min, the concentration of the zirconium sulfate gradually exceeds the solubility of the basic electrolyte, so that part of the zirconium sulfate is separated out and suspended in the electrolyte, the uniformity and stability of the electrolyte are influenced, the growth of a film layer is inhibited, and the thickness is reduced on the contrary.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface modification, and particularly relates to a preparation method and application of a wear-resistant composite gradient film layer on the surface of a titanium alloy. Background Art

[0002] Micro-arc oxidation technology is a means of in-situ ceramic oxide film growth modification implemented on the surfaces of non-ferrous metals such as aluminum, magnesium, zirconium, and titanium. The micro-arc oxidation film formed by this technology is mainly composed of metal oxides generated by the direct combination reaction of oxygen atoms and the metal matrix. Conducting micro-arc oxidation treatment on the metal surface can effectively improve its properties such as wear resistance, corrosion resistance, and high-temperature resistance. At the same time, the film layer generated by this technology is tightly combined with the metal matrix, and the combined product has a dense structure and high toughness.

[0003] Titanium alloys have attracted much attention due to their excellent comprehensive qualities, stable organizational structures, good toughness and plasticity, and good deformation ability at high temperatures. It can not only adapt to the process of hot pressure processing but also be strengthened by means such as quenching and aging. Nevertheless, the lower mechanical properties and poor wear resistance of titanium alloys limit their application scope and service life. Applying enhanced coatings on the material surface, such as boronizing or micro-arc oxidation technology, can enhance the wear resistance of its surface without damaging the properties of the main material, thereby extending the service life and reducing operating costs.

[0004] The traditional method of improving the surface film layer structure of titanium alloys by micro-arc oxidation uses different solution systems to prepare the film layer. The hardness of the micro-arc oxidation film layer of titanium alloys prepared in this way has been significantly improved, but the increase in the film layer hardness has also led to an increase in brittleness, and in some cases, it may cause the film layer to peel off.

[0005] Therefore, there is an urgent need to study a newer method for preparing the film layer. According to the formation mechanism of the micro-arc oxidation film layer, the addition amount of characteristic solutes is changed in real time to optimize the film layer structure and performance, and it is more firmly combined with the matrix to meet the harsh requirements of modern industrial society for the comprehensive performance of titanium alloy film layers. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art and provide a preparation method and application of a wear-resistant composite gradient film layer on the surface of a titanium alloy.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] On the one hand, the present invention provides a method for preparing a wear-resistant composite gradient film layer on the surface of a titanium alloy. First, zirconium element is introduced into the micro-arc oxidation process, and it reacts with oxygen element in the electrolyte to generate zirconium dioxide, which can significantly improve the hardness of the composite coating. Secondly, by changing the concentration of zirconium sulfate in the basic electrolyte, the concentration of zirconium element in the basic electrolyte is regulated, thereby affecting the content of zirconium dioxide in the film layer on the surface of the titanium alloy, and finally obtaining a titanium alloy with a surface composite gradient film layer; zirconium dioxide (ZrO2) is a high-hardness oxide.

[0009] Specifically, the preparation method specifically includes the following steps:

[0010] Step 1: Perform surface pretreatment on the titanium alloy to be treated; the pretreatment is specifically as follows: first, use ultrasonic waves to clean the surface of the titanium alloy to remove dirt, then perform mechanical polishing with silicon carbide water sandpaper, then use deionized water and anhydrous ethanol ultrasonic waves to remove the residual dirt on the surface of the titanium alloy, and finally perform drying for subsequent use;

[0011] Step 2: Place the pretreated titanium alloy to be treated as the anode into the pre-prepared basic electrolyte, and use stainless steel as the cathode; the components of the basic electrolyte specifically include: phosphoric acid is 3 - 20 g / L, sodium hexametaphosphate is 8 - 20 g / L, potassium bifluoride is 3 - 10 g / L, potassium dihydrogen phosphate is 3 - 10 g / L, and sodium citrate is 5 - 10 g / L;

[0012] Step 3: Use a micro-arc oxidation device to perform micro-arc oxidation treatment on the titanium alloy to be treated. At the same time, continuously drip a zirconium sulfate solution with a concentration of 100 - 110 g / L into the basic electrolyte for 13 - 17 min, with a dripping rate of 20 - 60 drops per minute, and stir for 15 - 18 min, finally obtaining a titanium alloy with a surface composite gradient film layer; the parameters of the micro-arc oxidation treatment are: voltage is 260 - 420 V, pulse frequency is 500 - 1000 Hz, duty cycle is 15% - 50%, time is 15 - 20 min, and the temperature of the electrolytic cell of the micro-arc oxidation device is at room temperature.

[0013] On the other hand, the present invention provides an application of a method for preparing a wear-resistant composite gradient film layer on the surface of a titanium alloy, which is applied to the preparation of a surface composite gradient film layer of a titanium alloy.

[0014] Compared with the prior art, the technical solution provided by the present invention includes the following beneficial effects:

[0015] The titanium alloy composite gradient film prepared by the present invention has high density and thickness, and shows an obvious evolution law: by dropping zirconium sulfate solution into the electrolyte, when the dropping time is 13 - 17 min, the film surface is smooth, the pores are small and uniform, and the thickness is appropriate; when the dropping time of zirconium sulfate solution is less than 13 min, the pores of the film increase and are uneven. At this time, the concentration of zirconium sulfate is small, and the generated ZrO2 is not enough to uniformly cover the surface of the titanium alloy, thus inhibiting the growth of the film and resulting in a small thickness; when the dropping time of zirconium sulfate solution is greater than 17 min, the concentration of zirconium sulfate gradually exceeds the solubility of the basic electrolyte, causing some zirconium sulfate to precipitate and suspend in the electrolyte, affecting the uniformity and stability of the electrolyte, inhibiting the growth of the film, and instead reducing the thickness.

[0016] Furthermore, through its unique in-situ growth mechanism and parameter controllability, the preparation method of the present invention provides an efficient and environmentally friendly solution for improving the wear resistance of the surface of materials such as titanium alloys, and shows significant advantages especially in solving the contradiction between hardness and brittleness and strengthening the film-substrate bonding force. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings here are incorporated into the specification and form a part of this specification, and are used together with the specification to explain the principles of the present invention.

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 is a flowchart of the preparation method of the present invention;

[0020] Figure 2 is an SEM image of the cross-section of the titanium alloy A composite gradient film in Example 1 of the present invention;

[0021] Figure 3 is an SEM image of the cross-section of the titanium alloy B composite gradient film in Example 2 of the present invention;

[0022] Figure 4 is an SEM image of the cross-section of the titanium alloy C composite gradient film in Example 3 of the present invention;

[0023] Figure 5 is an SEM image of the cross-section of the titanium alloy D composite gradient film in Comparative Example 1 of the present invention;

[0024] Figure 6 is an SEM image of the cross-section of the titanium alloy E composite gradient film in Comparative Example 2 of the present invention;

[0025] Figure 7 XRD pattern of the titanium alloy film layer in Embodiment 2 of the present invention;

[0026] Figure 8 Thickness variation diagram of the titanium alloy composite gradient film layers in Embodiments 1, 2, and 3 of the present invention;

[0027] Figure 9 Thickness variation diagram of the titanium alloy composite gradient film layers in Comparative Examples 1 and 2 of the present invention. Detailed implementation manners

[0028] Here, the exemplary embodiments will be described in detail, and the examples are shown in the accompanying drawings. The implementation manners described in the following exemplary embodiments do not represent all implementation manners consistent with the present invention. On the contrary, they are merely examples consistent with some aspects of the present invention detailed in the appended claims.

[0029] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

[0030] The present invention provides a method for preparing a wear-resistant composite gradient film layer on the surface of a titanium alloy. First, zirconium element is introduced into the micro-arc oxidation process to react with oxygen element in the electrolyte to generate zirconium dioxide, which can significantly improve the hardness of the composite coating. Secondly, by changing the concentration of zirconium sulfate in the basic electrolyte, the concentration of zirconium element in the basic electrolyte is regulated, thereby affecting the content of zirconium dioxide in the film layer on the surface of the titanium alloy, and finally obtaining a titanium alloy with a surface composite gradient film layer; zirconium dioxide (ZrO2) is a high-hardness oxide.

[0031] Specifically, the preparation method specifically includes the following steps:

[0032] Step 1. Perform surface pretreatment on the titanium alloy to be treated; the pretreatment is specifically as follows: first, use ultrasonic waves to clean the surface of the titanium alloy to remove dirt, then perform mechanical polishing with silicon carbide water sandpaper, then use deionized water and absolute ethanol ultrasonic waves to remove the residual dirt on the surface of the titanium alloy, and finally perform drying for subsequent use;

[0033] Step 2. Place the pretreated titanium alloy to be treated as the anode into the pre-prepared basic electrolyte, and use stainless steel as the cathode; the components of the basic electrolyte specifically include: phosphoric acid is 3 - 20 g / L, sodium hexametaphosphate is 8 - 20 g / L, potassium bifluoride is 3 - 10 g / L, potassium dihydrogen phosphate is 3 - 10 g / L, and sodium citrate is 5 - 10 g / L;

[0034] Step 3: Use a micro-arc oxidation device to perform micro-arc oxidation on the titanium alloy to be treated. At the same time, continuously drip a zirconium sulfate solution with a concentration of 100 - 110 g / L into the basic electrolyte for 13 - 17 minutes at a dripping rate of 20 - 60 drops per minute, and stir for 15 - 18 minutes to finally obtain a titanium alloy with a surface composite gradient film layer; the parameters of the micro-arc oxidation treatment are: voltage is 260 - 420 V, pulse frequency is 500 - 1000 Hz, duty cycle is 15% - 50%, time is 15 - 20 minutes, and the temperature of the electrolytic cell of the micro-arc oxidation device is at room temperature.

[0035] To verify the preparation method of the present invention, the inventor obtained five TC4 titanium alloy specimens with dimensions of 20 mm (length) × 20 mm (width) × 2 mm (thickness) by sawing and conducted the following experiments.

[0036] Example 1

[0037] See Figure 1 As shown, this example provides a preparation method for a wear-resistant composite gradient film layer on the surface of a titanium alloy, specifically including the following steps:

[0038] Step 1: Perform surface pretreatment on the TC4 titanium alloy specimen. Use ultrasonic waves to clean the titanium alloy specimen to remove dirt, and then successively use silicon carbide water sandpapers with 80 meshes, 240 meshes, 600 meshes, 1200 meshes, and 1500 meshes for mechanical polishing. Then, use deionized water and absolute ethanol for ultrasonic treatment for 5 minutes to remove the residual dirt on the surface of the titanium alloy specimen, and finally perform drying for subsequent use;

[0039] Step 2: First, place the pretreated titanium alloy specimen as the anode into 1 L of the pre-prepared basic electrolyte, and use stainless steel as the cathode; the components of the basic electrolyte are: potassium bifluoride is 3 g / L, sodium hexametaphosphate is 10 g / L, phosphoric acid is 3 g / L, potassium dihydrogen phosphate is 4 g / L, and sodium citrate is 5 g / L;

[0040] Step 3: Use a micro-arc oxidation device to perform micro-arc oxidation on the titanium alloy specimen. At the same time, continuously drip a zirconium sulfate solution with a concentration of 110 g / L into the basic electrolyte for 13 minutes at a dripping rate of 20 - 60 drops per minute, and stir for 15 minutes to finally obtain titanium alloy A with a surface composite gradient film layer; the voltage during the micro-arc oxidation treatment is 260 V, the pulse frequency is 1000 Hz, the duty cycle is 15%, and the time is 15 minutes.

[0041] Example 2

[0042] See Figure 1 As shown, this example provides a preparation method for a wear-resistant composite gradient film layer on the surface of a titanium alloy, specifically including the following steps:

[0043] Step 1: Perform surface pretreatment on the TC4 titanium alloy specimen. Use ultrasonic cleaning to remove dirt from the titanium alloy specimen, and then successively perform mechanical polishing with silicon carbide water sandpapers of 80 mesh, 240 mesh, 600 mesh, 1200 mesh, and 1500 mesh. Then, use deionized water and anhydrous ethanol for ultrasonic treatment for 5 minutes to remove the residual dirt on the surface of the titanium alloy specimen, and finally dry it for subsequent use;

[0044] Step 2: First, place the pretreated titanium alloy specimen as the anode into 1 L of pre-prepared basic electrolyte, and use stainless steel as the cathode; the composition of the basic electrolyte is: potassium bifluoride is 7 g / L, sodium hexametaphosphate is 14 g / L, phosphoric acid is 10 g / L, potassium dihydrogen phosphate is 6 g / L, and sodium citrate is 7 g / L;

[0045] Step 3: Use a micro-arc oxidation device to perform micro-arc oxidation treatment on the titanium alloy specimen. At the same time, continuously drip 15 min of zirconium sulfate solution with a concentration of 104 g / L into the basic electrolyte at a dripping rate of 20 - 60 drops per minute, and stir for 18 min to finally obtain titanium alloy B with a surface composite gradient film layer; the voltage of the micro-arc oxidation treatment is 350 V, the pulse frequency is 800 Hz, the duty cycle is 30%, and the time is 18 min.

[0046] Example 3

[0047] See Figure 1 As shown, this example provides a method for preparing a wear-resistant composite gradient film layer on the surface of a titanium alloy, which specifically includes the following steps:

[0048] Step 1: Perform surface pretreatment on the TC4 titanium alloy specimen. Use ultrasonic cleaning to remove dirt from the titanium alloy specimen, and then successively perform mechanical polishing with silicon carbide water sandpapers of 80 mesh, 240 mesh, 600 mesh, 1200 mesh, and 1500 mesh. Then, use deionized water and anhydrous ethanol for ultrasonic treatment for 5 minutes to remove the residual dirt on the surface of the titanium alloy specimen, and finally dry it for subsequent use;

[0049] Step 2: First, place the pretreated titanium alloy specimen as the anode into 1 L of pre-prepared basic electrolyte, and use stainless steel as the cathode; the composition of the basic electrolyte is: potassium bifluoride is 9 g / L, sodium hexametaphosphate is 19 g / L, phosphoric acid is 20 g / L, potassium dihydrogen phosphate is 10 g / L, and sodium citrate is 10 g / L;

[0050] Step 3: Use a micro-arc oxidation device to perform micro-arc oxidation treatment on the titanium alloy sample. At the same time, continuously drip a zirconium sulfate solution with a concentration of 100 g / L into the basic electrolyte for 17 minutes at a dripping rate of 20 - 60 drops per minute, and stir for 20 minutes to finally obtain titanium alloy C with a surface composite gradient film layer. The voltage during the micro-arc oxidation treatment is 400 V, the pulse frequency is 600 Hz, the duty cycle is 45%, and the time is 20 minutes.

[0051] Comparative Example 1

[0052] See Figure 1 As shown, this embodiment provides a method for preparing a wear-resistant composite gradient film layer on the surface of a titanium alloy, which specifically includes the following steps:

[0053] Step 1: Perform surface pretreatment on the TC4 titanium alloy sample. Use ultrasonic waves to clean the titanium alloy sample to remove dirt, and then successively perform mechanical polishing with silicon carbide water sandpapers of 80 mesh, 240 mesh, 600 mesh, 1200 mesh, and 1500 mesh. Then, use deionized water and absolute ethanol for ultrasonic treatment for 5 minutes to remove the residual dirt on the surface of the titanium alloy sample, and finally perform drying for subsequent use.

[0054] Step 2: First, place the pretreated titanium alloy sample as the anode into 1 L of the pre-prepared basic electrolyte, and use stainless steel as the cathode. The components of the basic electrolyte are: potassium bifluoride is 3 g / L, sodium hexametaphosphate is 10 g / L, phosphoric acid is 3 g / L, potassium dihydrogen phosphate is 4 g / L, and sodium citrate is 5 g / L.

[0055] Step 3: Use a micro-arc oxidation device to perform micro-arc oxidation treatment on the titanium alloy sample. At the same time, continuously drip a zirconium sulfate solution with a concentration of 104 g / L into the basic electrolyte for 10 minutes at a dripping rate of 20 - 60 drops per minute, and stir for 15 minutes to finally obtain titanium alloy D with a surface composite gradient film layer. The voltage during the micro-arc oxidation treatment is 350 V, the pulse frequency is 800 Hz, the duty cycle is 30%, and the time is 15 minutes.

[0056] Comparative Example 2

[0057] See Figure 1 As shown, this embodiment provides a method for preparing a wear-resistant composite gradient film layer on the surface of a titanium alloy, which specifically includes the following steps:

[0058] Step 1: Perform surface pretreatment on the TC4 titanium alloy sample. Use ultrasonic waves to clean the titanium alloy sample to remove dirt, and then successively perform mechanical polishing with silicon carbide water sandpapers of 80 mesh, 240 mesh, 600 mesh, 1200 mesh, and 1500 mesh. Then, use deionized water and absolute ethanol for ultrasonic treatment for 5 minutes to remove the residual dirt on the surface of the titanium alloy sample, and finally perform drying for subsequent use.

[0059] Step 2: First, take the pretreated titanium alloy sample as the anode and place it in 1 L of the pre-prepared basic electrolyte, and use stainless steel as the cathode; the basic electrolyte is: potassium bifluoride is 3 g / L, sodium hexametaphosphate is 10 g / L, phosphoric acid is 3 g / L, potassium dihydrogen phosphate is 4 g / L, and sodium citrate is 5 g / L;

[0060] Step 3: Use a micro-arc oxidation device to perform micro-arc oxidation treatment on the titanium alloy sample. At the same time, continuously drip a zirconium sulfate solution with a concentration of 104 g / L into the basic electrolyte for 20 min, at a rate of 20 - 60 drops per minute, and stir for 20 min to finally obtain titanium alloy E with a surface composite gradient film layer; the voltage during the micro-arc oxidation treatment is 350 V, the pulse frequency is 800 Hz, the duty cycle is 30%, and the time is 20 min.

[0061] To verify the effect of the preparation method of the present invention, electron microscope observations were made on the composite gradient film layers of titanium alloy A, titanium alloy B, titanium alloy C, titanium alloy D, and titanium alloy E respectively, and X-ray diffraction pattern observations were made on titanium alloy B, as Figures 2 to 9 shown:

[0062] Figures 2 to 6 Figure 14 is the SEM diagram of the surface composite gradient film layers of different titanium alloy samples prepared under different dropping times of the zirconium sulfate solution. The composite gradient film layer formed on the surface of the titanium alloy sample has a standard micro-arc oxidation film layer structure, and the surface of the film layer presents a porous shape. Moreover, according to the gradual increase in the dropping time of the zirconium sulfate solution, the surface film layer structure of the titanium alloy sample also changes significantly. It can be concluded that the surface structure of the film layer becomes gradually denser, the pore diameter gradually becomes smaller, and the distribution of pores gradually becomes denser as the dropping time of the zirconium sulfate solution increases; further, due to the gradual increase in the dropping time of the zirconium sulfate solution, the amount of Zr 4+ participating in the reaction also gradually increases, and the film layer thickness gradually increases. When the dropping time of zirconium sulfate increases to 20 min, the concentration of zirconium sulfate exceeds the solubility of the basic electrolyte, resulting in the precipitation of part of the zirconium sulfate, affecting the stability of the electrolyte, and inhibiting the growth of the film layer, and the thickness decreases instead.

[0063] Figure 7 Figure 20 is the XRD diagram of the surface composite gradient film layer of the titanium alloy sample in Example 2. It can be seen that ZrO2, ZrTiO4, and TiO2 exist in the prepared composite gradient film layer, among which the content of ZrTiO4 is the largest, and the contents of ZrO2 and TiO2 are uniform, which greatly improves the anti-friction property of the film layer.

[0064] Figure 8 and Figure 9It is a graph showing the thickness change of the titanium alloy composite gradient film layer. From this, it can be seen that as the dropping time of the zirconium sulfate solution increases, the thickness of the film layer observed in the cross-section of the titanium alloy sample composite gradient film layer also increases. It can be seen that the maximum thickness of the micro-arc oxidation film layer in Example 1 is 6.80 μm, the maximum thickness of the micro-arc oxidation film layer in Example 2 is 9.47 μm, the maximum thickness of the micro-arc oxidation film layer in Example 3 is 5.07 μm, the maximum thickness of the micro-arc oxidation film layer in Comparative Example 1 is 4.17 μm, and the maximum thickness of the micro-arc oxidation film layer in Comparative Example 2 is 3.45 μm; that is, the thickness of the micro-arc oxidation film layer prepared by this preparation method is greater than 5 μm.

[0065] In summary, when preparing the composite gradient film layer by this preparation method, when the dropping time of the zirconium sulfate solution is 13 - 17 min, the surface of the composite gradient film layer formed on the titanium alloy surface is smooth, the pores are small and uniform, and the thickness is appropriate, meeting the use requirements.

[0066] It should also be noted that the film formation mechanism on the surface of the titanium alloy sample is as follows: The morphology structure and tissue composition of the titanium alloy micro-arc oxidation film layer are closely related to the composition of the electrolyte. In the anodic region during the micro-arc oxidation process, when titanium dissolves from the substrate, the reaction occurs:

[0067] Ti → Ti 4+ +4e -

[0068] Ti 4+ +4OH - → TiO2 + 2H2O

[0069] The additive Zr(SO4)2 reacts in the alkaline electrolyte as follows:

[0070] Zr 4+ +4OH - → ZrO2 + 2H2O

[0071] The above are only the specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0072] It should be understood that the present invention is not limited to the above-described content and can be modified and changed without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. A method for preparing a wear-resistant composite gradient film on a titanium alloy surface, characterized in that: First, the zirconium element is introduced into the micro-arc oxidation process to react with the oxygen element in the electrolyte to form zirconium dioxide, which can improve the hardness of the composite coating. Then, the concentration of zirconium sulfate in the base electrolyte is changed to control the concentration of zirconium in the base electrolyte, thereby affecting the content of zirconium dioxide in the surface film layer of the titanium alloy, and finally a titanium alloy with a surface composite gradient film layer is obtained.

2. The preparation method according to claim 1, characterized in that: The specific steps include: Step 1, performing surface pretreatment on the titanium alloy to be treated; Step 2, placing the pretreated titanium alloy to be treated as an anode into a pre-prepared basic electrolyte; Step 3: Perform micro-arc oxidation treatment on the titanium alloy to be treated using a micro-arc oxidation device, while continuously adding a zirconium sulfate solution to the base electrolyte for a specific time and stirring, to finally obtain a titanium alloy with a surface composite gradient film layer.

3. The preparation method according to claim 2, characterized in that: In step 1, the pretreatment is specifically as follows: first, the titanium alloy surface is cleaned with ultrasound to remove dirt, then mechanically polished with silicon carbide water sandpaper, then ultrasonically cleaned with deionized water and anhydrous ethanol to remove residues on the titanium alloy surface, and finally dried for subsequent use.

4. The preparation method according to claim 2, characterized in that: In step 2, the ingredients of the basic electrolyte specifically include: 3-20 g / L phosphoric acid, 8-20 g / L sodium hexametaphosphate, 3-10 g / L potassium bifluoride, 3-10 g / L potassium dihydrogen phosphate, and 5-10 g / L sodium citrate.

5. The preparation method according to claim 2, characterized in that: In step 3, the parameters of the micro-arc oxidation treatment are: voltage of 260-420V, pulse frequency of 500-1000Hz, duty cycle of 15%-50%, and time of 15-20min.

6. The preparation method according to claim 2, characterized in that: In step 3, the concentration of the zirconium sulfate solution is 100-110 g / L.

7. The preparation method according to claim 2, characterized in that: In step 3, the dropping rate of the zirconium sulfate solution is 20 to 60 drops per minute, and the dropping time is 13 to 17 minutes.

8. The preparation method according to claim 2, characterized in that: In step 3, the stirring time is 15 to 20 minutes.

9. The use of the preparation method according to any one of claims 1 to 8, characterized in that: Used in the preparation of composite gradient film on titanium alloy surface.

Images