Method for realizing corrosion resistance treatment on titanium alloy surface by laminated ironing and electrodeposition

Abstract

The present invention discloses a method for achieving corrosion resistance treatment on the surface of titanium alloy by means of laminated ironing and electrodeposition. First, the surface of the titanium alloy substrate is subjected to laminated ironing to form a nanocrystalline transition layer on the surface, increasing the dislocation density and introducing appropriate internal stress, effectively enhancing the surface residual stress of the titanium alloy. Then, the surface is polished at low frequency to obtain a reasonable surface roughness and improve the electrochemistry deposition reaction activity. Then, electrochemical deposition surface treatment is carried out. Sodium sulfate, methanol and titanium dioxide nanoparticles are added to the electrochemistry deposition solution to improve the deposition efficiency of the electrochemistry coating. The method of the present invention improves the corrosion resistance of the titanium alloy. The electrochemical impedance is increased by two orders of magnitude, the corrosion potential is shifted positively, the corrosion current density is reduced by two orders of magnitude, and the integrity of the electrodeposition coating is improved, reducing the coating defects.

Description

Technical Field

[0001] The present invention relates to a surface treatment method for titanium alloys, and more particularly, to a surface treatment technology that combines a stacked ironing process and an electrochemical deposition process to improve the corrosion resistance treatment of the titanium alloy surface. Background Art

[0002] Titanium and its alloys (such as TC4) are widely used in the aerospace field and the ship field due to their excellent mechanical properties, fatigue resistance, and corrosion resistance. However, with the wide application of titanium alloys, the failure modes have become diversified. In environments with high humidity, high chloride ion content, and strong solar radiation, such as the marine atmospheric environment, there are still serious corrosion damages. Therefore, it is necessary to apply a corrosion-resistant coating to the titanium alloy for protection.

[0003] In the preparation process of the corrosion-resistant coating, the electrodeposition technology has obvious advantages due to its good control of dimensional accuracy, low roughness, high density, and low cost. However, the traditional electrodeposition process has problems such as large surface roughness of the substrate, uneven surface texture of the substrate, small surface residual stress, and surface defects, resulting in insufficient bonding strength between the coating and the substrate, slow nucleation rate and growth rate of the coating, and inability to guarantee the coating uniformity. Therefore, appropriate pretreatment is a prerequisite for obtaining a good electrodeposited layer on the titanium alloy surface.

[0004] At present, the electrodeposition pretreatment of titanium alloys often adopts methods such as anodic oxidation, sandpaper friction, acid etching, and alkali etching. Although these methods can quickly and inexpensively remove the stains and oxide films on the titanium alloy surface and reduce the coating difficulty, they cannot solve the problems of large surface roughness, uneven texture, small residual stress, and many coating defects of the titanium alloy surface, resulting in a small bonding strength between the coating and the substrate, slow nucleation rate and growth rate of the coating, and inability to meet the large-scale processing requirements. Summary of the Invention

[0005] In order to improve the corrosion resistance of the titanium alloy surface and solve the problem of poor integrity of the electrodeposited coating on the titanium alloy, the present invention proposes a method for achieving corrosion resistance treatment on the titanium alloy surface by means of stacked ironing and electrodeposition. First, the surface of the titanium alloy substrate is subjected to stacked ironing to form a nanocrystalline transition layer on the surface, with the dislocation density increasing by 2-3 orders of magnitude and introducing an appropriate internal stress of -300 MPa to -800 MPa, laying a foundation for the electrochemical coating deposition. Then, the surface is polished at a low frequency to obtain a reasonable surface roughness with Ra of 0.6 μm to 1.2 μm and improve the electrochemical deposition reaction activity. Finally, electrochemical deposition treatment is carried out. Sodium sulfate, methanol, and titanium dioxide nanoparticles are added to the electrochemical deposition solution to improve the deposition efficiency of the electrochemical coating. Sodium sulfate acts as a supporting electrolyte to reduce the influence of electromigration in the solution on the electrode reaction rate; methanol can inhibit the occurrence of the side reaction of hydrogen evolution reaction, improve the current efficiency during the deposition process, and reduce defects such as pinholes in the coating; titanium dioxide nanoparticles adsorb on the electrode surface to form heterogeneous nucleation sites, accelerating the deposition process of the coating on the electrode surface. The results show that the method provided by the present invention effectively improves the corrosion resistance of the titanium alloy, with the electrochemical impedance increasing by 2 orders of magnitude, the corrosion potential shifting positively, the corrosion current density decreasing by 2 orders of magnitude, and improving the integrity of the electrodeposited coating, reducing coating defects.

[0006] A method for achieving corrosion resistance treatment on the titanium alloy surface by means of stacked ironing and electrodeposition proposed by the present invention is a pretreatment process added before electrochemical deposition to improve the corrosion resistance of the electrochemical deposited coating; it is characterized by including the following steps:

[0007] Step 1, the same-pass multi-stack ironing process;

[0008] According to the stacked ironing trajectory, the ironing treatment of the titanium alloy surface is carried out to obtain an ironed titanium alloy specimen;

[0009] Description of the stacked ironing trajectory: As the machine tool starts, the tool gradually feeds; at the beginning and end of the ironing, only the outermost edge area of the tool is ironed once; during the stacked ironing process, the ironing marks of the next circle partially cover the ironing marks of the previous circle, and are subjected to multiple superimposed ironing processes during the same-pass machining;

[0010] The tool on the ironing machine is cylindrical with a radius of 2 mm, and the tool is made of synthetic diamond;

[0011] Stacked ironing parameters: the ironing depth is 0.010 mm to 0.020 mm, the rotational speed is 160 rev / min to 1000 rev / min, the feed rate is 0.005 mm / rev to 0.020 mm / rev, the processing temperature is 20 °C to 40 °C, and the coolant is liquid nitrogen;

[0012] The residual stress on the surface of the substrate treated by the laminar ironing is -200 MPa to -1000 MPa;

[0013] Step Two, low-frequency grinding and ultrasonic cleaning;

[0014] Step 21, low-frequency grinding, the grinding frequency is 0.5 Hz to 1 Hz, and the rod-shaped titanium alloy specimen is ground with 1000# to 3000# silicon carbide sandpaper to obtain a ground titanium alloy specimen; the grinding direction is parallel to the axial direction of the titanium alloy rod-shaped specimen, and when the grinding frequency is less than 1 Hz, the surface roughness of the specimen is controlled to be 0.6 μm to 1.2 μm;

[0015] Step 22, ultrasonic cleaning, the ultrasonic frequency is set to 20 kHz to 40 kHz; the ground titanium alloy specimen is ultrasonically cleaned in acetone solution for 5 min to 30 min first, and then ultrasonically cleaned in absolute ethanol solution for 5 min to 30 min to obtain a clean titanium alloy specimen;

[0016] Step Three, electrochemical deposition treatment;

[0017] Composition of the electrodeposition solution: 0.32 g to 1.60 g of titanium oxysulfate, 0.07 g to 0.34 g of hydrogen peroxide, 1.01 g to 6.07 g of potassium nitrate, 2.84 g to 14.20 g of sodium sulfate, and 0.16 g to 0.80 g of titanium dioxide nanoparticles are added to a 200 mL solution formed by 100 mL of methanol and 100 mL of deionized water;

[0018] Electrochemical deposition process: the electrodeposition time is 2000 s to 5000 s, the electrodeposition potential is -0.6 V to -1.2 V, and the electrodeposition mode is the potentiostatic mode;

[0019] The electrochemical deposition process is carried out on an electrochemical workstation; a three-electrode system is set up, where the reference electrode is a saturated calomel electrode, the counter electrode is a platinum sheet electrode, and the working electrode is a clean titanium alloy specimen; electrochemical deposition is carried out according to the electrochemical deposition process to obtain a titanium alloy surface with an electrochemical coating.

[0020] The advantages of the method for realizing corrosion resistance treatment on the surface of titanium alloy by laminar ironing and electrodeposition of the present invention are as follows:

[0021] ① Laminar ironing: First, laminar ironing treatment is carried out on the surface of the titanium alloy, which effectively improves the bonding force between the titanium alloy and the electrochemical deposition layer. A nanocrystalline transition layer is formed on the surface of the titanium alloy through the laminar ironing process, and surface nanocrystallization is more conducive to the growth of the coating. On the other hand, the transition layer generated by laminar ironing also increases the density of the coating and reduces its defects, thereby improving its corrosion resistance protection effect.

[0022] ②In the process sequence of the present invention, the titanium alloy is first pretreated by stacked ironing and then electrochemically deposited, resulting in fewer defects in the deposited coating and further improving the corrosion resistance of the titanium alloy surface.

[0023] ③In the present invention, sodium sulfate is added as a supporting electrolyte to the titanium dioxide electrochemically deposited solution to reduce the influence of electromigration in the solution on the electrode reaction rate.

[0024] ④In the present invention, methanol is added to the titanium dioxide electrochemically deposited solution to inhibit the occurrence of the side reaction of hydrogen evolution reaction, improve the current efficiency of the deposition process, and reduce defects such as pinholes in the coating.

[0025] ⑤In the present invention, titanium dioxide nanoparticles are added to the titanium dioxide electrochemically deposited solution, which is conducive to the adsorption of titanium dioxide nanoparticles on the electrode surface to form heterogeneous nucleation sites and accelerate the deposition process of the coating on the electrode surface. Description of the Drawings

[0026] Figure 1 is a flow chart of the corrosion resistance treatment of the titanium alloy surface by stacked ironing and electro-deposition of the present invention.

[0027] Figure 2 is a schematic diagram of the multi-stack ironing trajectory of the same pass of the present invention.

[0028] Figure 3 is the residual stress map of the TC4 titanium alloy surface after multi-stack ironing of the same pass in Examples 1-8 of the present invention.

[0029] Figure 4 is the XRD pattern of the sample treated by the method of Example 1 and the original TC4 alloy.

[0030] Figure 5 is the charge transfer resistance map of Examples 1-8 of the present invention.

[0031] Figure 6 is the corrosion potential E corr and the corrosion current density i corr diagram.

[0032] Figure 7 is the defect concentration of Examples 1-8 of the present invention.

[0033] Figure 8 is the surface SEM diagram of the original TC4 alloy and Example 1 immersed for 168 h under ultraviolet radiation.

[0034] Figure 9 is the change of the charge transfer resistance R ct with the immersion time in Examples 1, 3 and 7 under ultraviolet radiation.

[0035] Figure 10 The defect concentrations N of Examples 1, 3, and 7 under ultraviolet radiation D vary with the immersion time. Detailed implementation manners

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0037] To improve the corrosion resistance of the titanium alloy surface during the electrochemical deposition process and to address the problem of poor integrity of the electroplated coating on the titanium alloy, refer to Figure 1 as shown, the present invention proposes a method for improving the corrosion resistance treatment of the titanium alloy surface by using stacked ironing and electrochemical deposition, including the following steps:

[0038] Step 1, the same-pass multi-stack ironing process;

[0039] In the present invention, the titanium alloy surface is ironed according to the stacked ironing trajectory to obtain an ironed titanium alloy specimen.

[0040] The tool on the ironing machine is cylindrical with a radius of 2 mm, and the tool is made of synthetic diamond.

[0041] Stacked ironing parameters: the ironing depth is 0.010 mm to 0.020 mm, the rotational speed is 160 rev / min to 1000 rev / min, the feed rate is 0.005 mm / rev to 0.020 mm / rev, the processing temperature is 20°C to 40°C, and the coolant is liquid nitrogen.

[0042] In the present invention, the number of stacked ironing times in the same-pass stacked ironing is 1 to 90 times.

[0043] After the titanium alloy surface is treated by the same-pass multi-stack ironing process, a titanium dioxide transition layer with a nanocrystalline structure is formed. Measured by X-ray diffraction method, the residual stress of the transition layer is -200 MPa to -1000 MPa. The formation of a nanocrystalline transition layer on the titanium alloy surface through the stacked ironing process makes surface nanocrystallization more conducive to the growth of the coating. On the other hand, the transition layer generated by the stacked ironing also increases the density of the coating, reduces coating defects, and thus improves the corrosion resistance protection effect.

[0044] In the present invention, the stacked ironing trajectory is formed by setting a larger ironing depth and a smaller feed rate, so that the ironing marks of the next circle partially cover the ironing marks of the previous circle during the stacked ironing process, and the covered area of the ironing marks is subjected to multiple superimposed ironing processes during the same-pass processing. Compared with the traditional ironing method, this same-pass multi-stack ironing trajectory improves the efficiency of nanocrystal preparation, introduces greater residual stress, and reduces the surface roughness after processing. It can effectively reduce the number of processing passes while introducing a thicker deformation layer and appropriate internal stress, and improve the efficiency of the ironing process.

[0045] In the present invention, the stacked ironing treatment on the surface of the titanium alloy substrate is carried out in a lathe CM0420M / 2. After installing the specimen, set the ironing depth, rotational speed and feed rate according to the stacked ironing trajectory, and start the machine tool for ironing processing. In the present invention, the shape of the titanium alloy processed specimen is rod-shaped or disc-shaped.

[0046] Step two, low-frequency grinding and ultrasonic cleaning;

[0047] Step 21, low-frequency grinding, the grinding frequency is 0.5 Hz to 1 Hz, and a 1000# to 3000# silicon carbide sandpaper is used to perform low-frequency grinding on the rod-shaped titanium alloy specimen to obtain a ground titanium alloy specimen. The grinding direction is parallel to the axial direction of the rod-shaped titanium alloy specimen. When the grinding frequency is less than 1 Hz, control the surface roughness of the specimen so that the arithmetic mean deviation of the profile Ra is 0.6 μm to 1.2 μm, preferably 0.86 μm.

[0048] Step 22, ultrasonic cleaning, set the ultrasonic frequency to 20 kHz to 40 kHz; first ultrasonically clean the ground titanium alloy specimen in an acetone solution (volume fraction of 99.96%) for 5 min to 30 min, and then ultrasonically clean it in an absolute ethanol solution (volume fraction of 99.5%) for 5 min to 30 min to obtain a clean titanium alloy specimen.

[0049] In the present invention, low-frequency grinding can effectively retain the appropriate residual stress on the surface of the ironed specimen after the stacked ironing in step one, and at the same time obtain a reasonable surface roughness and make the surface roughness uniform, avoiding the singularities and surface damage that may occur during the low-frequency grinding machining process of titanium alloy, so that the surface is not too smooth or too rough, improving the electro-deposition reaction activity, making the electro-deposited surface denser, and reducing the defects of the electro-deposited coating. Ultrasonic cleaning is to remove the oil and contaminants on the surface of the titanium alloy before electro-deposition.

[0050] Step three, electrochemical deposition treatment;

[0051] Composition of the electro-deposition solution: Add 0.32 g to 1.60 g of titanium oxysulfate, 0.07 g to 0.34 g of hydrogen peroxide, 1.01 g to 6.07 g of potassium nitrate, 2.84 g to 14.20 g of sodium sulfate, and 0.16 g to 0.80 g of titanium dioxide nanoparticles to a 200 mL solution formed by 100 mL of methanol and 100 mL of deionized water.

[0052] Electrochemical deposition process: The electro-deposition time is 2000 s to 5000 s, the electro-deposition potential is -0.6 V to -1.2 V, and the electro-deposition mode is a constant potential mode.

[0053] In the present invention, the electrochemically deposition process is carried out on a CHI 660E electrochemical workstation from Shanghai Chenhua. A three-electrode system is set up, where the reference electrode is a saturated calomel electrode, the counter electrode is a platinum sheet electrode, and the working electrode is a clean titanium alloy specimen; electrochemical deposition is carried out according to the electrochemically deposition process to obtain a titanium alloy surface with an electrochemical coating.

[0054] In the present invention, sodium sulfate is added to the electrodeposition solution as a supporting electrolyte, which is beneficial to reducing the influence of electromigration in the solution on the electrode reaction rate. Titanium dioxide nanoparticles are added to enable the titanium dioxide nanoparticles to adsorb on the electrode surface to form heterogeneous nucleation sites and accelerate the deposition of the coating on the electrode surface. Methanol is added to inhibit the hydrogen evolution reaction during the electrodeposition process and reduce coating defects.

[0055] Example 1

[0056] Ironing is carried out on a lathe with the model CM0420M / 2 according to the stacked ironing process conditions. The TC4 alloy bar is fixed on the lathe, and a synthetic diamond tool is used for stacked ironing processing, with liquid nitrogen as the coolant. Among them, the tool is cylindrical with a radius of 2 mm. The ironing depth, rotation speed, feed rate, and number of passes are set to 0.020 mm, 800 rev / min, 0.005 mm / rev, and 1 time respectively; then the machine tool is started for stacked ironing treatment to obtain an ironed TC4 titanium alloy specimen.

[0057] According to the Figure 2 shown in the stacked ironing trajectory, as the machine tool starts, the tool gradually feeds, and the number of times the TC4 alloy bar is subjected to stacked ironing is 1 - 90 times. Figure 2 (a) shows that only the outermost edge area of the tool is subjected to 1 ironing at the start and end of ironing. For other areas, due to the large ironing depth and small feed rate, the ironing marks of the next circle partially cover the ironing marks of the previous circle during the stacked ironing process, and multiple superimposed ironing processes are received during the same pass processing. Figure 2 (b) shows the situation where 40 times of stacked ironing are received in the area near the starting point or the ending point of the tool at the start and end of ironing, while Figure 2 (c) shows the ironing trajectory of the area where 90 times of stacked ironing can be fully carried out as the tool moves after ironing for a period of time.

[0058] The stacked ironed TC4 alloy specimen is wire-cut into specimens with dimensions of 0.5 cm × 1 cm × 0.1 cm. Under a polishing frequency of 1 Hz, it is polished from 180# to 2000# with SiC sandpaper, and the roughness of the polished specimen is 0.86 μm. The back of the specimen is adhered to the copper wire with copper powder conductive adhesive, and then sealed with epoxy resin, and the exposed working surface is 0.5 cm 2Before use, the resistance between one end of the wire and the working surface of each sealed specimen was measured with an ohmmeter to ensure good connection between the specimen and the wire and reduce experimental errors. After the specimens were prepared, they were successively cleaned with acetone and absolute ethanol for 5 minutes each at an ultrasonic frequency of 20 kHz and then dried to obtain clean TC4 titanium alloy specimens.

[0059] 0.64 g of titanium oxysulfate, 0.20 g of hydrogen peroxide, 2.02 g of potassium nitrate, 7.10 g of sodium sulfate and 0.48 g of titanium dioxide nanoparticles were added to a 200 mL solution formed by 100 mL of methanol and 100 mL of deionized water.

[0060] The clean TC4 titanium alloy specimens were electrochemically deposited with titanium dioxide in the electroplating solution. They were placed in the electroplating solution at room temperature and electroplated in the constant potential mode with a deposition potential of -1 V and a deposition time of 3000 s. After electroplating with titanium dioxide, the TC4 alloy specimens were washed with deionized water and dried at room temperature.

[0061] Example 2

[0062] The difference between Example 2 and Example 1 is that the ironing depth, rotation speed, feed rate and number of passes set in Example 2 are 0.015 mm, 800 rev / min, 0.005 mm / rev and 1 time respectively. The roughness of the polished specimen is 0.70 μm.

[0063] 0.96 g of titanium oxysulfate, 0.30 g of hydrogen peroxide, 3.03 g of potassium nitrate, 10.65 g of sodium sulfate and 0.72 g of titanium dioxide nanoparticles were added to a 200 mL solution formed by 100 mL of methanol and 100 mL of deionized water.

[0064] Example 3

[0065] The difference between Example 3 and Example 1 is that the ironing depth, rotation speed, feed rate and number of passes set in Example 3 are 0.010 mm, 800 rev / min, 0.005 mm / rev and 1 time respectively. The roughness of the polished specimen is 1.2 μm.

[0066] Example 4

[0067] The difference between Example 4 and Example 1 is that the ironing depth, rotation speed, feed rate and number of passes set in Example 4 are 0.015 mm, 160 rev / min, 0.005 mm / rev and 1 time respectively. The roughness of the polished specimen is 0.80 μm.

[0068] Example 5

[0069] Example 5 is different from Example 1 in that the ironing depth, rotation speed, feed rate, and number of passes set in Example 5 are 0.015 mm, 500 rev / min, 0.005 mm / rev, and 1 pass respectively. The roughness of the polished specimen is 0.86 μm.

[0070] Example 6

[0071] Example 6 is different from Example 1 in that the ironing depth, rotation speed, feed rate, and number of passes set in Example 6 are 0.015 mm, 1000 rev / min, 0.005 mm / rev, and 1 pass respectively. The roughness of the polished specimen is 0.95 μm.

[0072] Example 7

[0073] Example 7 is different from Example 1 in that the ironing depth, rotation speed, feed rate, and number of passes set in Example 7 are 0.015 mm, 800 rev / min, 0.010 mm / rev, and 1 pass respectively. The roughness of the polished specimen is 1.1 μm.

[0074] Add 0.32 g of titanium oxysulfate, 0.10 g of hydrogen peroxide, 1.01 g of potassium nitrate, 3.55 g of sodium sulfate, and 0.24 g of titanium dioxide nanoparticles to a 200 mL solution formed by 100 mL of methanol and 100 mL of deionized water.

[0075] Example 8

[0076] Example 8 is different from Example 1 in that the ironing depth, rotation speed, feed rate, and number of passes set in Example 8 are 0.015 mm, 800 rev / min, 0.015 mm / rev, and 1 pass respectively. The roughness of the polished specimen is 1.0 μm.

[0077] Analysis of Ironing Surface Performance

[0078] The multi-stack ironing process in the same pass can introduce residual compressive stress in the grain refinement area on the material surface. Compared with shot peening technology, rolling and other large plastic deformations, the residual compressive stress introduced by the multi-stack ironing process in the same pass is higher, deeper, and more stable. The residual stress of the ironed titanium alloy prepared in Examples 1-8 was measured by X-ray diffraction method, and the residual stress was tested using an X-ray stress tester of model X-3000 produced by AST StressTech. The test parameters were: scanning step size 0.033°, counting time 100 s, tube voltage 45 kV, and tube current 40 mA.

[0079] Test Results Figure 3 As shown in, from Table 1 and Figure 3It can be concluded that the residual compressive stress on the ironing surface in Examples 1 to 8 generally shows a trend of first decreasing and then increasing, and the range of residual stress is from -200 MPa to -1000 MPa. When the rotational speed and ironing depth are kept fixed and the feed rate increases, the surface residual stress increases accordingly. When the rotational speed and feed rate are constant, the surface residual stress first increases and then decreases with the increase of the ironing depth. When the feed rate and ironing depth are fixed, with the increase of the rotational speed, the change of the surface residual stress is relatively complex, showing a trend of first increasing, then decreasing, and then increasing again.

[0080] Grain size

[0081] The surface ironing process realizes the nanocrystallization of the material surface grains and the increase of the dislocation density. On the one hand, during the processing, the high-hardness cutting tool tip can apply a large compressive stress on the material surface, and the high rotational speed of the machine tool can increase the deformation rate of the material, causing severe plastic deformation on the material surface and generating a large number of dislocations. The dislocations entangle with each other to form dislocation cells. When the energy of the dislocation cells is greater than the grain boundary energy, the dislocation cells will transform into sub-boundaries. With the increase of the number of grain boundaries, the surface grains continue to refine. On the other hand, due to the low-temperature environment of liquid nitrogen providing a large degree of supercooling, rapid nucleation of grains occurs, and there is not enough time for growth, further refining the grains. In order to study the material phase of the ironed surface, it is necessary to perform X-ray diffraction analysis (XRD) on the material to calculate the surface grain size and dislocation density. When X-rays, as an electromagnetic wave, are projected onto a crystal, they will be scattered by the atoms in the crystal, and the scattered waves are like spherical waves emitted from the atomic centers. Since the atoms are arranged periodically in the crystal, there is a fixed phase relationship between these scattered spherical waves, which will cause the spherical waves in some scattering directions to reinforce each other and cancel each other in some directions, resulting in the diffraction phenomenon. The internal atomic arrangement of each crystal is different, so the corresponding diffraction patterns are also different, similar to human fingerprints, so phase analysis can be carried out. Among them, the distribution law of the diffraction lines in the diffraction pattern is determined by the size, shape and orientation of the unit cell. The intensity of the diffraction lines is determined by the types of atoms and their positions in the unit cell.

[0082] The X-ray diffractometer used is the D / max2500PC automatic X-ray diffractometer produced by Rigaku Corporation of Japan. The target material is a Cu target, its scanning voltage is 40 kV, scanning current is 200 mA, scanning speed is 6° / min, and the scanning range of 2θ is 30° to 90°. The test results Figure 4As shown, where (a) and (b) are the XRD patterns of the as - received TC4 alloy and Example 1 respectively. The overall morphology of the XRD patterns in both states is basically the same, including the α - phase and β - phase. The difference is that for the as - received specimen, each diffraction peak is high and sharp. Compared with the as - received TC4 alloy in Example 1, the intensity of each diffraction peak decreases and all diffraction peaks are broadened, indicating that the surface grains of the specimen have been significantly refined. According to X - ray diffraction theory, when the grain size is less than 100 nm, the smaller the grain size, the more obvious the broadening of its diffraction peak. At this time, the Scherrer formula can be used to calculate the grain size. Through calculation, the grain size of Example 1 is 17.14 nm.

[0083] Analysis of the corrosion resistance of the electrochemically deposited surface

[0084] The electrochemically deposited coatings of the titanium alloys in Examples 1 - 8 were subjected to electrochemical impedance spectroscopy (EIS) tests in a 3.5 wt% NaCl solution. Before the EIS test, an open - circuit potential test was carried out for 1800 s to stabilize the system. The test frequency range was from 100 kHz to 0.01 Hz. The measured EIS data was fitted using ZSimpWin software according to the selected equivalent circuit to obtain the parameters of the interfacial electrochemical reaction. For Examples 1 - 8, the EIS spectra were fitted with an equivalent circuit with two time constants. Among them, R s represents the solution resistance (Ω·cm 2 ), R1 represents the capacitance of the coating (Ω·cm 2 ), which can represent the charge - transfer resistance on the specimen surface. Q1 represents the capacitance of the coating (μF·cm －2 ), R ct represents the resistance of the double - layer (MΩ·cm 2 ), Q c represents the capacitance of the double - layer (μF·cm －2 ), x 2 represents the EIS fitting error (10 －2 ). In the equivalent - circuit fitting of the EIS spectra, n1 and n2 are dimensionless parameters representing the deviation from the pure - capacitance property of two constant - phase elements; when n1 = 1 or n2 = 1, the constant - phase element has the pure - capacitance property, and when n1 = 0 or n2 = 0, the constant - phase element has the pure - resistance property.

[0085] Table 2 Fitting data of the electrochemically deposited coatings of the titanium alloys prepared in Examples 1 - 8

[0086] Serial number <![CDATA[R s > <![CDATA[R1]]> <![CDATA[Q1]]> <![CDATA[n1]]> <![CDATA[R ct > <![CDATA[Q c > <![CDATA[n2]]> <![CDATA[x 2 > Example 1 9.58 6.02 10.23 0.81 160.22 6.32 0.88 0.2 Example 2 9.45 5.45 9.61 0.85 115.63 8.98 0.86 0.4 Example 3 8.99 5.69 9.45 0.84 100.46 10.91 0.91 0.3 Example 4 8.57 5.64 9.98 0.59 135.12 10.67 0.79 0.1 Example 5 8.79 4.98 9.77 0.65 91.65 16.51 0.75 0.2 Example 6 9.65 2.55 7.55 0.85 16.32 17.66 0.85 0.4 Example 7 8.36 2.11 7.35 0.66 11.22 21.32 0.88 0.3 Example 8 8.92 2.15 6.97 0.72 6.87 29.31 0.84 0.1

[0087] As can be seen from the parameters of the equivalent - circuit fitting of the EIS in Table 2, for Examples 1 - 8, R sBasically similar, and the value of n2 is also very close, indicating that Examples 1 to 8 have similar capacitance characteristics on the surface. By observing Figure 5 Charge transfer resistance R ct the data, it is found that the charge transfer resistance R of Example 1 ct is 160.22 MΩ·cm 2 , which is 381.47 times higher than that of the original TC4 alloy of 0.42 MΩ·cm 2 . The charge transfer resistances of Examples 1 to 8 are all higher than that of the original TC4 alloy, indicating that the degree of hindrance to electron migration is stronger and the corrosion resistance is improved. However, it may be due to the too low residual stress on the surfaces of Examples 2 and 3 and the too high residual stress on the surfaces of Examples 6 to 8, resulting in the improvement effects of these samples being inferior to those of Examples 1 and 4.

[0088] The potentiodynamic polarization curve (PDP) is obtained by setting a scanning speed at a certain electrode potential. This scanning speed changes with a relatively slow change value and measures the instantaneous current value at the corresponding potential. The instantaneous current is plotted against the corresponding electrode potential to obtain the entire polarization curve. The corrosion current density and corrosion potential of the system can be obtained according to the Tafel extrapolation method. These are two key parameters for evaluating the corrosion resistance of the system. Generally, it is considered that the smaller the corrosion current density value, the smaller the corrosion rate, and the more positive the corrosion potential value, the smaller the corrosion tendency, and the better the corrosion resistance of the system. The polarization curve tests were carried out on the electrodeposited coatings of the titanium alloys prepared in Examples 1 to 8 in a 3.5 wt% NaCl solution. The starting potential of the test was -0.8 V, the ending potential was +0.8 V, the scanning speed was 0.001 V / s, and the sensitivity was 10 －6 .

[0089] Table 3 Test results of the polarization curves of the electrodeposited coatings of the titanium alloys prepared in Examples 1 to 8

[0090] Specimen <![CDATA[E corr (V)]]> <![CDATA[i corr (A / cm 2 )]]> Example 1 －0.24 <![CDATA[1.25×10 －8 > Example 2 －0.39 <![CDATA[3.23×10 －8 > Example 3 －0.62 <![CDATA[7.94×10 －8 > Example 4 －0.27 <![CDATA[1.25×10 －8 > Example 5 －0.37 <![CDATA[4.78×10 －8 > Example 6 －0.49 <![CDATA[1.49×10 －7 > Example 7 －0.63 <![CDATA[1.99×10 －7 > Example 8 －0.76 <![CDATA[1.25×10 －6 >

[0091] The test results are shown in Table 3 and Figure 6 as follows. According to the Tafel extrapolation method, the corrosion current (i corr ) and corrosion potential (E corr ) of the samples were calculated. Among them, the average values of E corr and i corr of the original TC4 titanium alloy were -0.56 V and 5.97×10 － 6 A / cm -2 . Among Examples 1 to 8, the corrosion current density of the sample in Example 1 is the smallest, and i corr is reduced to 1.20×10 －8 A / cm－2 , compared with the original TC4 sample i corr About 2 orders of magnitude lower; Example 4 sample is second, i corr Reduced to 1.61×10 －8 A / cm －2 The corrosion current density of Examples 1 to 8 is less than that of the original TC4 titanium alloy. corr The E of the original TC4 alloy sample is -0.24V. corr The positive shift is about 0.32V, and the positive shift of the sample of Example 4 is about 0.29V, indicating that the corrosion tendency is reduced under the test conditions, while the E corr A negative shift occurs, indicating that the corrosion tendency increases. Therefore, in an aggressive environment, the corrosion rates of Examples 1 to 8 are reduced compared to the original TC4 titanium alloy, but the residual compressive stress of Example 3 is too small, and the residual compressive stress of Examples 7 and 8 is too large, resulting in a positive shift in the corrosion potential and an increase in the corrosion tendency. The titanium alloy electroplated coatings prepared in Examples 1 to 8 were subjected to a Mott-Schottky curve test in a 3.5wt% NaCl solution. The test frequency was 1kHz, and the test potential was -1V to 1.5V. The test results are shown in Tables 4 and Figure 6 shown.

[0092] Table 4 Defect concentration data obtained by calculating the slope of the linear fitting curve of the MS curve of the titanium alloy electrodeposited coatings prepared in Examples 1 to 8

[0093]

[0094]

[0095] The test results are shown in Table 4 and Figure 7 As shown, the defect concentration of the sample in Example 1 is the lowest, which is 5.29×10 18 cm －3 , is the original TC4 sample 67.08×10 18 cm －3 The sample of Example 4 was second, which was 7.17×10 18 cm -3 , which is 10.7% of the original TC4 sample. Since the residual compressive stress of Examples 2 and 3 is too low, and the residual compressive stress of Examples 6 to 8 is too high, the defect concentration of the samples is higher than that of Examples 1 and 4, but all are higher than the original TC4 sample. This shows that appropriate residual stress improves the density of the coating deposition and reduces defects. It can be seen that the samples after the same-pass stacking ironing and electroplating treatment can obtain a smaller defect concentration. Combined with the EIS test and polarization curve test, the test trend rules obtained are basically consistent, both indicating better corrosion resistance.

[0096] Analysis of surface stability of electrochemical deposition under long-term ultraviolet irradiation environment

[0097] The chemical stability and UV corrosion resistance of the samples were investigated under UV conditions. A 15W UV lamp was used for irradiation, with irradiation for 12 hours per day and a 12-hour period without light. The solution used was a 3.5wt% NaCl solution. The experimental temperature was set at 25.0°C, the humidity was 97.0%, and ventilation was maintained throughout the experiment.

[0098] Figure 8 (a) and (b) are the surface morphologies of the original TC4 alloy and the sample of Example 1 after being immersed in UV radiation for 168 hours. After the original TC4 alloy sample was immersed in UV radiation for 168 hours, the sample surface was obviously uneven, with a large amount of granular and flaky materials distributed, severe corrosion cracking, and peeling, which confirmed the effect of UV radiation on the corrosion resistance of the original TC4 material. The surface morphology of the sample of Example 1 immersed in UV radiation for 168 hours is shown in Figure 1. Figure 8 As shown in (b), the surface morphology is smooth and flat on the whole, with no protrusions or grooves, and basically no corrosion cracking or peeling. After immersion for 168 hours, the surface is still very flat, with only a few corrosion pits, showing good chemical stability. Ultraviolet radiation has almost no significant effect on the composite coating system of Example 1, which also confirms that the same-pass multi-layer ironing and electrodeposition process can provide good protection for the substrate.

[0099] Analysis of corrosion resistance of electrochemically deposited surfaces under long-term ultraviolet irradiation

[0100] Electrochemical impedance spectroscopy (EIS) was performed on the samples of Examples 1, 3, and 7 immersed in a 3.5 wt% NaCl solution under UV irradiation. The test solution was a 3.5 wt% NaCl solution at a temperature of 25°C. ZSimpWin software was used to fit the EIS patterns to obtain parameters of the interfacial electrochemical reaction. For Examples 1, 3, and 7, an equivalent circuit with two time constants was used to fit the EIS patterns.

[0101] Table 5 Long-term electrochemical characteristics of the coatings obtained in Examples 1, 3, and 7 under ultraviolet irradiation

[0102] ​ <![CDATA[R s > <![CDATA[R1]]> <![CDATA[Q1]]> <![CDATA[n1]]> <![CDATA[R ct > <![CDATA[Q c > <![CDATA[n2]]> <![CDATA[x 2 > ​ 10.68 2.72 3.47 0.52 160.62 8.38 0.84 0.22 ​ 10.25 2.88 3.83 0.78 167.81 9.61 0.84 0.35 ​ 10.67 2.53 3.64 0.69 180.66 9.15 0.74 0.27 ​ 10.10 2.78 3.97 0.37 199.18 9.68 0.80 0.18 ​ 10.85 2.31 3.79 0.36 235.69 9.12 0.74 0.36 ​ 7.28 2.18 3.55 0.63 100.46 6.68 0.77 0.29 ​ 8.74 3.21 3.92 0.53 107.98 7.77 0.68 0.54 ​ 9.97 3.45 3.47 0.49 119.21 6.99 0.77 0.17 ​ 9.15 4.66 3.45 .66 125.56 7.89 0.83 0.35 ​ 9.87 2.67 3.78 0.48 150.65 8.56 0.70 0.11 ​ 7.78 2.47 3.67 0.58 11.87 9.67 0.71 0.36 ​ 7.69 2.78 3.55 0.53 15.67 9.12 0.69 0.12 ​ 7.47 2.58 3.32 0.57 21.29 9.74 0.65 0.25 ​ 9.63 2.83 3.67 0.78 29.12 9.21 0.62 0.18 ​ 7.52 2.85 3.30 0.79 33.67 9.47 0.78 0.11

[0103] Electrochemical performance after immersion

[0104] The equivalent circuit fitting results are shown in Table 5 and ​As shown, it can be found that under ultraviolet irradiation, the charge transfer resistance of the specimens of Examples 1, 3, and 7 is significantly greater than that of the original specimens. With the increase of the soaking time, the charge transfer resistance value gradually rises. The charge transfer resistance value of the specimen of Example 1 is significantly greater than that of Example 3 and Example 7, indicating an increase in the resistance of the electrochemical corrosion reaction. After soaking for 168 h, the charge transfer resistance R ct of Example 1 is 235.69 MΩ·cm 2 is four orders of magnitude higher than the charge transfer resistance R ct of the original TC4 alloy specimen, which is 0.022 MΩ·cm 2 The improvement is huge. The charge transfer resistances of Examples 3 and 7 are also greater than that of the original TC4 alloy specimen, indicating that the specimen system after multi-layer ironing and electrochemical deposition treatment in the same pass can still maintain excellent corrosion resistance under the dual action of ultraviolet irradiation and corrosive medium.

[0105] The specimens of Examples 1, 3, and 7 were tested for Mott-Schottky curves in a 3.5 wt% NaCl solution. The test frequency was 1 kHz, and the test potential was from -1 V to 1.5 V.

[0106] The test results are as ​ shown. The specimen of Example 1 has the lowest defect concentration, which is 5.52×10 18 cm -3 , which is 3.58% of the defect concentration of the original TC4 specimen, 154.03×10 18 cm -3 . Due to the too low residual compressive stress in Example 3 and the too high residual compressive stress in Example 7, the defect concentration of the specimens is higher than that of Example 1, but both are lower than that of the original TC4 specimen. It shows that appropriate residual stress improves the deposition density of the coating and reduces the defects. It can be seen that the samples treated by multi-layer ironing and electro-deposition in the same pass can obtain a smaller defect concentration. Combined with the EIS test and polarization curve test, the obtained test trend rules are basically the same, all indicating better corrosion resistance. It is proved that the enhancement effect brought by the multi-layer ironing and electro-deposition process in the same pass improves the resistance of the material under ultraviolet irradiation conditions and obtains lower defects. Compared with ​ , the defect concentrations of Examples 1, 3, and 7 increase slightly, indicating that the dual action of ultraviolet irradiation and corrosive medium will damage the coating on the material surface and accelerate the failure of the material.

Claims

1. A method for achieving corrosion resistance treatment on the surface of titanium alloy by means of laminated ironing and electrodeposition, which is a pretreatment process added before electrodeposition in order to improve the corrosion resistance of the electrochemically deposited coating; characterized in that It includes the following steps: Step 1, multi-layer ironing process in the same pass; According to the multi-layer ironing trajectory, perform ironing treatment on the surface of the titanium alloy to obtain an ironed titanium alloy sample; Description of the multi-layer ironing trajectory: As the machine tool starts, the tool gradually feeds; at the beginning and end of ironing, only the outermost edge area of the tool is ironed once; during the multi-layer ironing process, the ironing marks of the next circle partially cover the ironing marks of the previous circle, and multiple superimposed ironing processes are performed during the same-pass processing; The tool on the ironing machine is cylindrical with a radius of 2 mm, and the tool is made of synthetic diamond; Multi-layer ironing parameters: ironing depth is 0.010 mm to 0.020 mm, rotational speed is 160 rev / min to 1000 rev / min, feed rate is 0.005 mm / rev to 0.020 mm / rev, processing temperature is 20°C to 40°C, and the coolant is liquid nitrogen; The residual stress on the surface of the multi-layer ironed substrate is -200 MPa to -1000 MPa; Step 2, low-frequency grinding and ultrasonic cleaning; Step 21, low-frequency grinding, the grinding frequency is 0.5 Hz to 1 Hz, use 1000# to 3000# silicon carbide sandpaper to perform low-frequency grinding on the rod-shaped titanium alloy sample to obtain a ground titanium alloy sample; the grinding direction is parallel to the axial direction of the titanium alloy rod-shaped sample, and when the grinding frequency is less than 1 Hz, control the surface roughness of the sample to be 0.6 μm to 1.2 μm; Step 22, ultrasonic cleaning, set the ultrasonic frequency to 20 kHz to 40 kHz; first perform ultrasonic cleaning on the ground titanium alloy sample in acetone solution for 5 min to 30 min, and then perform ultrasonic cleaning in anhydrous ethanol solution for 5 min to 30 min to obtain a clean titanium alloy sample; Step 3, electrochemical deposition treatment; Composition of the electrodeposition solution: Add 0.32 g to 1.60 g of titanium oxysulfate, 0.07 g to 0.34 g of hydrogen peroxide, 1.01 g to 6.07 g of potassium nitrate, 2.84 g to 14.20 g of sodium sulfate, and 0.16 g to 0.80 g of titanium dioxide nanoparticles to a 200 mL solution formed by 100 mL of methanol and 100 mL of deionized water; Electrochemical deposition process: The electrodeposition time is 2000 s to 5000 s, the electrodeposition potential is -0.9 V to -1.2 V, and the electrodeposition mode is the potentiostatic mode; The electrochemical deposition process is carried out on an electrochemical workstation; set up a three-electrode system, where the reference electrode is a saturated calomel electrode, the counter electrode is a platinum sheet electrode, and the working electrode is a clean titanium alloy sample; perform electrochemical deposition according to the electrochemical deposition process to obtain a titanium alloy surface with an electrochemical coating.

2. The method for achieving corrosion-resistant treatment on the surface of titanium alloy by means of laminated ironing and electrodeposition according to claim 1, characterized in that: In the same pass of multi-layer ironing, the number of multi-layer ironing times is 1 to 90 times.

3. The method for achieving corrosion resistance treatment on the surface of titanium alloy by laminated ironing and electrodeposition according to claim 1, wherein: The shape of the titanium alloy sample during multi-layer ironing is rod-shaped or disc-shaped.

4. The method for achieving corrosion resistance treatment on the surface of titanium alloy by means of laminated ironing and electrodeposition according to claim 1, characterized in that: Through low-frequency grinding, the residual stress on the surface of the ironed sample after ironing can be effectively retained.

5. The method for realizing corrosion resistance treatment on the surface of titanium alloy by laminated ironing and electrodeposition according to claim 1, wherein: Through multi-layer ironing and electrodeposition, the surface grains of the titanium alloy are nano-sized and the dislocation density increases, and the grain size is 10 nm to 30 nm.

6. The method for achieving corrosion resistance treatment on the surface of titanium alloy by means of laminated ironing and electroplating according to claim 1, characterized in that: Through multi-layer ironing and electrodeposition, the corrosion resistance of the titanium alloy surface is improved by two orders of magnitude.

7. The method for achieving corrosion resistance treatment on the surface of titanium alloy by means of laminated ironing and electrodeposition according to claim 1, characterized in that: The surface of titanium alloy is improved in the stability of the electrochemically deposited surface under long-term ultraviolet irradiation environment through laminated ironing and electrodeposition.

8. The method for achieving corrosion resistance treatment on the surface of titanium alloy by means of laminated ironing and electrodeposition according to claim 1, characterized in that: The surface of titanium alloy is improved in the corrosion resistance of the electrochemically deposited surface under long-term ultraviolet irradiation environment through laminated ironing and electrodeposition.

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