Method for preparing electromagnetic wave absorbing ceramic coating on surface of titanium alloy

Abstract

The invention discloses a method for preparing an electromagnetic wave absorbing ceramic coating on a titanium alloy surface. The method comprises the following steps that (1) titanium alloy pretreatment is conducted, specifically, grinding and polishing and ultrasonic oil removal are conducted; 2) preparing a micro-arc oxidation solution; and 3) performing micro-arc oxidation treatment by controlling electrical parameters. The method is simple and controllable in process, easy to implement and suitable for large-scale industrial application. The prepared coating has wave absorbing performance, good corrosion resistance and high hardness, and the main components of the coating comprise titanium dioxide (rutile phase and anatase phase) and aluminum titanate. And high bonding strength and structural stability are achieved between the coating and the base body, and the corrosion resistance of the titanium alloy is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional coatings, and particularly relates to a method for preparing an electromagnetic wave absorbing ceramic coating on the surface of a titanium alloy. Background Art

[0002] With the continuous deepening of various research works carried out by countries around modern warfare, military stealth technology has developed rapidly. Nowadays, making fighter jets have radar stealth characteristics is the key R & D direction of each country, and preparing an absorbing coating on the surface of a substrate to meet the corresponding stealth performance requirements is one of the most effective methods. There are many methods for preparing absorbing coatings, such as physical coating method, spraying method, electroless plating method, magnetron sputtering method, etc. However, most coatings have low adhesion to the substrate and poor protection for the substrate, which will cause the coating to fall off and fail, and the multiple stacked coatings result in a relatively thick thickness, violating the lightweight design requirements of fighter jets.

[0003] Titanium metal matrix composites play an increasingly important role in the fields of automobiles and aerospace due to their unique advantages such as high specific strength, excellent high-temperature performance, and high specific modulus. In the aviation field, they can be used to manufacture aircraft engine blades and airframe structural components, such as skeletons, cabin doors, landing gears, etc. Micro-arc oxidation is usually used to prepare oxide films on the surfaces of valve metals such as Al, Mg, and Ti. The oxide film formed by this technology has excellent corrosion resistance, high hardness, good wear resistance, and bonding strength. By adjusting process parameters and electrolyte components, the performance of the oxide film can be optimized and the thickness of the oxide film is easy to control. Moreover, the ceramic coating formed by the micro-arc oxidation process has a porous characteristic, and the rich micro-pores are beneficial to the multiple reflections of electromagnetic waves and are beneficial to the consumption of electromagnetic energy. Although the micro-arc oxidation technology has many advantages mentioned above, there are still few research reports on preparing stealth absorbing coatings using this technology at present. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems that the existing electromagnetic wave absorbing coatings have low adhesion to the substrate, relatively thick thickness, and unqualified corrosion resistance, and a method for preparing an electromagnetic wave absorbing coating on the titanium base by micro-arc oxidation is designed and developed.

[0005] A method for preparing an electromagnetic wave absorbing ceramic coating on the surface of a titanium alloy is specifically completed according to the following steps:

[0006] (1) Pretreatment of titanium alloy: Use sandpaper to polish the titanium alloy until the surface reaches mirror finish to obtain a titanium alloy with a bright surface; Immerse the titanium alloy with a bright surface in absolute ethanol, perform ultrasonic cleaning treatment, then rinse the titanium alloy with distilled water, and then dry it to obtain a dry titanium alloy;

[0007] (2) Prepare the electrolyte solution: Stir and ultrasonically treat the reagent and deionized water at room temperature to obtain a uniformly mixed solution;

[0008] (3) Micro-arc oxidation: Use a surface-cleaned and dried titanium alloy substrate as the anode and a stainless steel plate as the cathode. Immerse the cathode and anode in the above-prepared electrolyte. Under the constant voltage mode, adjust the electrical parameters to perform micro-arc oxidation treatment to prepare a coating on the surface of the titanium substrate.

[0009] Further, in step (1), the size of the titanium alloy is 30 mm × 30 mm × 3 mm, and a small hole is reserved in the upper middle of the plate; successively use SiO sandpapers with particle sizes of 120#, 180#, 400#, 600#, 800#, and 1000# to polish the titanium alloy until the surface reaches a mirror finish. 2

[0010] Further, in step (1), the power of the ultrasonic treatment is 100 W, and the ultrasonic treatment time is 10 min to 20 min.

[0011] Further, in step (1), use distilled water to thoroughly rinse the titanium alloy 3 to 5 times, and then use a hair dryer to dry it to obtain the degreased titanium alloy.

[0012] Further, in step (2), the electrolyte solution includes 10 g / L sodium metaaluminate, 1 g / L sodium hydroxide, and 4 g / L carbonyl iron powder.

[0013] Further, in step (2), the stirring time is 10 to 30 min, and it is only carried out when the electrolyte is sodium metaaluminate and sodium hydroxide. After the stirring is completed, add carbonyl iron powder and perform ultrasonic treatment for 10 to 30 min.

[0014] Further, in step (3), the micro-arc oxidation treatment process adopts the constant voltage mode. The micro-arc oxidation electrical parameters include: positive duty cycle 10% to 25%, positive termination voltage 250 to 350 V, negative duty cycle 10% to 25%, negative termination voltage 50 V, current frequency 400 Hz, micro-arc oxidation reaction time 10 to 40 min, and temperature 20 to 40 °C.

[0015] Advantages of the present invention:

[0016] ​The coating provided by the present invention is formed on the surface of the substrate through in-situ growth. The inner layer has a dense structure, and its main components include titanium dioxide (mainly rutile phase and anatase phase) and aluminum titanate, endowing the titanium alloy with good corrosion resistance and high hardness. The outer layer has a uniform crater-like structure with interconnected pores. The coating has a high bonding strength and structural stability with the substrate, is not prone to peeling, and has good mechanical properties. Moreover, the present invention provides precise parameter ranges, including voltage, current, frequency, duty cycle, and reaction time, to achieve precise control of the micro-arc oxidation process and ensure the uniformity and consistency of the coating. The process of the present invention is simple and controllable, easy to implement, and convenient for large-scale industrial application. Description of the Drawings

[0017] Figure 1 SEM image of the titanium alloy microwave-absorbing ceramic coating obtained by the method of Example 1.

[0018] Figure 2 SEM image of the titanium alloy microwave-absorbing ceramic coating obtained by the method of Example 2.

[0019] Figure 3 Microhardness diagram of the coatings in Examples 1-4.

[0020] Figure 4 Three-dimensional perspective view of the reflection loss of the titanium alloy microwave-absorbing ceramic coating obtained by the method of the experimental example at different thicknesses and frequencies.

[0021] Figure 5 Potentiodynamic polarization curves of the control example, Example 4, and TC4 substrate. Detailed Embodiments

[0022] The present invention will be further described in detail below with reference to the drawings and embodiments:

[0023] The present invention designs and develops a method for preparing a microwave-absorbing ceramic coating on the surface of a titanium alloy. The present invention uses the micro-arc oxidation method to generate a microwave-absorbing coating in an alkaline electrolyte, including electrolyte components, electrical parameters, and specifically includes the following steps:

[0024] Step 1. Specimen preparation and pretreatment: The titanium alloy used in the present invention is a commercially available titanium alloy. The size of the titanium alloy is cut into 30 mm × 30 mm × 3 mm, and a small hole is reserved in the upper middle of the plate. The titanium alloy is polished successively with SiO 2 sandpapers with particle sizes of 120#, 180#, 400#, 600#, 800#, and 1000# until the surface reaches mirror finish. The titanium alloy with a bright surface is immersed in absolute ethanol for ultrasonic cleaning treatment, then rinsed with distilled water, and then dried to obtain a dry titanium alloy for use.

[0025] Step 2: Configure the alkaline electrolyte: Weigh 15 g of sodium aluminate and 1 g of sodium hydroxide, add them to 500 ml of deionized water, and stir for 10 - 30 min. After complete mixing, add 4 g of carbonyl iron powder, sonicate for 10 - 30 min, and then make up the volume to 1 L.

[0026] Step 3: Micro-arc oxidation: Pass a titanium wire with a diameter of 0.5 - 0.8 mm through the pre-treated square holes of the titanium alloy sample, hang the sample on the titanium wire, and immerse it in the electrolyte in the electrolytic cell. Then, set the micro-arc oxidation power supply parameters, including the forward current, forward voltage, reverse voltage, working frequency, duty cycle, number of pulses, and micro-arc oxidation time. During the experiment, use an electrolyte stirring device to ensure uniform distribution of the electrolyte, and control the electrolyte temperature below 40 °C through a circulating cooling water device.

[0027] Step 4: Post-treatment of micro-arc oxidation: After the voltage drops to 0 V, take out the sample, ultrasonically clean it successively with deionized water and absolute ethanol, and then air-dry it naturally.

[0028] The micro-arc oxidation electrical parameters described in Step 3 include: adopting a constant voltage mode, with a forward duty cycle of 10% - 25%, a forward termination voltage of 250 - 350 V, a reverse duty cycle of 10% - 25%, a reverse termination voltage of 50 V, a current frequency of 400 Hz, and a micro-arc oxidation reaction time of 10 - 40 min.

[0029] Testing method

[0030] Surface morphology and element content testing: In this experiment, a JSM-IT500HR type electron microscope was used to photograph and observe the surface and cross-sectional morphology of the coating, with a scanning voltage of 10 kV. With the assistance of the supporting Energy Dispersive X-ray Spectroscopy (EDS), the types and compositions of the elements in the coating were analyzed.

[0031] Coating thickness testing: Use a K6-C type multi-functional coating thickness gauge to measure the thickness of the micro-arc oxidation coating. Before testing, zero-calibrate the thickness gauge using the titanium alloy substrate. During testing, place the probe vertically on the object to be measured and gently press to start the measurement. Randomly select 10 positions for multiple measurements to ensure data reliability.

[0032] Coating hardness testing: Use an HVS-1000Z type microhardness tester to measure the microhardness of the coating surface. Randomly select 10 points from different positions, exclude the maximum and minimum values, and then calculate the average value of the remaining points. The applied load during testing is 0.5 kg, and the continuous loading time is 15 s.

[0033] Electrochemical corrosion test: The obtained coating was tested and analyzed for its potentiodynamic polarization curve using an electrochemical workstation (Zahner Zennium Pro) to evaluate the corrosion resistance of the specimen. The electrochemical test was carried out in an electrochemical workstation with a three-electrode system. The specimen to be tested was the working electrode, the platinum electrode was the counter electrode, and the saturated calomel electrode was the reference electrode. The corrosion solution used in the test was 3.5 wt% NaCl corrosion solution, and the test was carried out at room temperature. The scanning range of the potentiodynamic polarization curve was -1 V to 1 V, and the scanning rate was 1 mV / s. The corrosion potential and corrosion current density of the specimen could be obtained according to the anodic polarization curve and cathodic polarization curve in the Tafel region of the curve.

[0034] Electromagnetic wave absorption performance test: The electromagnetic parameters of the sample were measured using an E5071C vector network analyzer. The synthesized experimental sample was mixed with paraffin in a specific mass ratio and heated to ensure uniform distribution. The mixture was placed into a special mold and pressed into a ring-shaped sample with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. The S parameters of the sample were measured in the frequency range of 2 to 18 GHz using the coaxial method, and the complex permittivity and complex permeability of the sample were calculated through professional software. According to the transmission line theory, the reflection loss of the sample was further calculated.

[0035] Next, the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0036] Example 1

[0037] A method for preparing an electromagnetic wave-absorbing ceramic coating on the surface of a titanium alloy in this embodiment is carried out according to the following steps:

[0038] (1) Specimen pretreatment: The TC4 plate was polished successively with 120#, 180#, 400#, 600#, 800# and 1000# SiO 2 sandpaper, then immersed in absolute ethanol for ultrasonic cleaning, and then rinsed with distilled water and dried to obtain a dry titanium alloy for standby.

[0039] (2) The electrolyte ratio was as follows: the concentration of sodium metaaluminate was 15 g / L, the concentration of sodium hydroxide was 1 g / L, and the concentration of carbonyl iron powder was 4 g / L.

[0040] (3) Micro-arc oxidation settings: The positive voltage was 350 V, the negative voltage was 50 V, the duty cycle was 20%, and the frequency was 400 Hz; and the micro-arc oxidation reaction time was 30 min, and the temperature was below 40 °C. After micro-arc oxidation, when the voltage dropped to 0 V, the specimen was taken down and ultrasonically cleaned successively with deionized water and absolute ethanol, and then air-dried.

[0041] Performance Test and Results of the Coating:

[0042] Figure 1 SEM image of the titanium alloy microwave-absorbing ceramic coating prepared for Example 1.

[0043] The thickness of the coating is 16.93 μm.

[0044] The microhardness of the coating is 492.71 HV 0.5 .

[0045] When the matching thickness of the coating is 2.5 mm, the effective absorption bandwidth below -10 dB is 0.12 GHz; when the matching thickness is 2.7 mm, the reflection loss reaches the minimum value of -14.38 dB at 12.4 GHz.

[0046] Example 2

[0047] A method for preparing an electromagnetic wave-absorbing ceramic coating on the surface of a titanium alloy in this example is carried out according to the following steps:

[0048] (1) Specimen pretreatment: The TC4 plate is polished successively with 120#, 180#, 400#, 600#, 800# and 1000# SiO 2 sandpaper, then immersed in absolute ethanol for ultrasonic cleaning, and then rinsed with distilled water and dried to obtain a dry titanium alloy for standby.

[0049] (2) The electrolyte ratio is as follows: the concentration of sodium metaaluminate is 15 g / L, the concentration of sodium hydroxide is 1 g / L, and the concentration of carbonyl iron powder is 4 g / L.

[0050] (3) Micro-arc oxidation setting of electrical parameters: the positive voltage is 300 V, the negative voltage is 50 V, the duty cycle is 25%, and the frequency is 400 Hz; and the micro-arc oxidation reaction time is 30 min, and the temperature is below 40 °C. After micro-arc oxidation, when the voltage drops to 0 V, the specimen is taken down and ultrasonically cleaned successively with deionized water and absolute ethanol, and then air-dried.

[0051] Performance Test and Results of the Coating:

[0052] Figure 2 SEM image of the titanium alloy microwave-absorbing ceramic coating prepared for Example 2.

[0053] The thickness of the coating is 12.23 μm.

[0054] The microhardness of the coating is 462.79 HV 0.5 .

[0055] The reflection loss of the coating did not exhibit an effective absorption bandwidth within the matching thickness range of 1 - 5 mm; when the matching thickness was 2.8 mm, the reflection loss reached a minimum value of -7.98 dB at 12.36 GHz.

[0056] Example 3

[0057] A method for preparing an electromagnetic wave absorbing ceramic coating on the surface of a titanium alloy in this example is carried out according to the following steps:

[0058] (1) Specimen pretreatment: The TC4 plate was polished successively with 120#, 180#, 400#, 600#, 800# and 1000# SiO 2 sandpaper, then immersed in absolute ethanol for ultrasonic cleaning, then rinsed with distilled water and dried to obtain a dry titanium alloy for standby.

[0059] (2) The electrolyte formulation was as follows: the concentration of sodium metaaluminate was 15 g / L, the concentration of sodium hydroxide was 1 g / L, and the concentration of carbonyl iron powder was 4 g / L.

[0060] (3) Micro-arc oxidation settings: the positive voltage was 300 V, the negative voltage was 50 V, the duty cycle was 20%, and the frequency was 400 Hz; and the micro-arc oxidation reaction time was 40 min, with the temperature below 40 °C. After micro-arc oxidation, when the voltage dropped to 0 V, the specimen was taken out and ultrasonically cleaned successively with deionized water and absolute ethanol, and then air-dried.

[0061] Coating performance test and results:

[0062] The thickness of the coating was 11.10 μm.

[0063] The microhardness of the coating was 430.15 HV 0.5 .

[0064] When the matching thickness of the coating was 2.8 mm, the effective absorption bandwidth was only 0.08 GHz; when the matching thickness was 2.9 mm, the reflection loss reached a minimum value of -11.19 dB at 12.28 GHz.

[0065] Example 4

[0066] A method for preparing an electromagnetic wave absorbing ceramic coating on the surface of a titanium alloy in this example is carried out according to the following steps:

[0067] (1) Specimen pretreatment: The TC4 plate was polished successively with 120#, 180#, 400#, 600#, 800# and 1000# SiO 2 sandpaper, then immersed in absolute ethanol for ultrasonic cleaning, then rinsed with distilled water and dried to obtain a dry titanium alloy for standby.

[0068] (2) The electrolyte formulation is as follows: the concentration of sodium aluminate is 15 g / L, the concentration of sodium hydroxide is 1 g / L, and the concentration of carbonyl iron powder is 4 g / L.

[0069] (3) The electrical parameters for micro-arc oxidation are set as follows: the positive voltage is 300 V, the negative voltage is 50 V, the duty cycle is 20%, and the frequency is 400 Hz; and the micro-arc oxidation reaction time is 30 min, and the temperature is below 40 °C. After micro-arc oxidation, when the voltage drops to 0 V, the sample is taken off and ultrasonically cleaned successively with deionized water and absolute ethanol, and then air-dried.

[0070] Performance testing and results of the coating:

[0071] The thickness of the coating is 10.61 μm.

[0072] The microhardness of the coating is 453.85 HV 0.5 。

[0073] When the matching thickness of the coating is 2.6 mm, the effective absorption bandwidth of the reflection loss is 0.20 GHz; when the matching thickness is 3.2 mm, the reflection loss reaches the minimum value of -34.23 dB at 13.72 GHz. Figure 4 It is a three-dimensional view of the reflection loss of the coating at different thicknesses and frequencies.

[0074] Control example

[0075] A method for preparing an electromagnetic wave absorbing ceramic coating on the surface of a titanium alloy in this control example is carried out according to the following steps:

[0076] (1) The TC4 plate of the sample is successively polished with 120#, 180#, 400#, 600#, 800# and 1000# SiO2 sandpapers, then immersed in absolute ethanol for ultrasonic cleaning, and then rinsed with distilled water and dried to obtain a dry titanium alloy for standby.

[0077] (2) The electrolyte formulation is as follows: the concentration of sodium aluminate is 15 g / L, and the concentration of sodium hydroxide is 1 g / L.

[0078] (3) The electrical parameters for micro-arc oxidation are set as follows: the positive voltage is 300 V, the negative voltage is 50 V, the duty cycle is 20%, and the frequency is 400 Hz; and the micro-arc oxidation reaction time is 30 min, and the temperature is below 40 °C. After micro-arc oxidation, when the voltage drops to 0 V, the sample is taken off and ultrasonically cleaned successively with deionized water and absolute ethanol, and then air-dried.

[0079] Performance testing and results of the coating:

[0080] The thickness of the coating is 7.7 μm.

[0081] The microhardness of the coating is 377 HV 0.5 .

[0082] The reflection loss of the coating did not show an effective absorption bandwidth within the matching thickness range of 1 - 5 mm; when the matching thickness was 2.6 mm, the reflection loss reached a minimum value of -2.68 dB at 13.84 GHz Figure 5 The potentiodynamic polarization curves of the control example, Example 4, and the TC4 substrate are shown

[0083] The results of the coating thickness, hardness, and wave absorption performance of the above examples are summarized in Table 1

[0084] Table 1 Coating thickness, hardness, and wave absorption performance of the coating

[0085]

[0086] The potentiodynamic polarization curves and the corresponding data fitting results of the control example, Example 4, and the TC4 substrate specimens are shown in Table 2

[0087] Table 2 Data fitting results of the potentiodynamic polarization curves of different specimens

[0088] <![CDATA[E corr (V)]]> <![CDATA[I corr (μA·cm 2 )]]> <![CDATA[β a (mV / dec)]]> <![CDATA[β c (mV / dec)]]> <![CDATA[R p (ohm·cm 2 )]]> TC4 -0.33766 1.30590 528.30 454.07 8.1194E+4 Control Example -0.29047 1.12720 493.23 396.05 8.4618E+4 Example 4 -0.16449 0.59117 435.52 391.15 1.5158E+5

[0089] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. The content of this specification should not be construed as a limitation on the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included within the protection scope of the claims of the present invention

Claims

1. A method for preparing an electromagnetic wave absorbing ceramic coating on a titanium alloy surface, characterized in that: The method comprises the following steps: (1) Pretreatment of titanium alloy: grinding and polishing the titanium alloy with sandpaper until the surface reaches mirror finish to obtain a titanium alloy with a bright surface; immersing the titanium alloy with a bright surface in anhydrous ethanol for ultrasonic cleaning, then rinsing the titanium alloy with distilled water, and then drying to obtain a dry titanium alloy; (2) preparing an electrolyte solution containing carbonyl iron powder: stirring the reagent and deionized water under ultrasonic conditions at room temperature to obtain a uniform mixed solution; (3) Micro-arc oxidation: A clean and dry titanium alloy substrate is used as the anode and a stainless steel plate is used as the cathode. The cathode and the anode are immersed in the prepared electrolyte containing carbonyl iron powder. Under constant voltage mode, the electrical parameters are adjusted to perform micro-arc oxidation treatment to prepare a coating on the surface of the titanium substrate.

2. The method according to claim 1, characterized in that: In step (1), the size of the titanium alloy is 30 mm × 30 mm × 3 mm, and a small hole is reserved in the upper middle part of the plate; the titanium alloy is polished using SiO2 sandpaper with particle sizes of 120#, 180#, 400#, 600#, 800# and 1000# in sequence until the surface reaches a mirror finish.

3. The method according to claim 1, characterized in that: In step (1), the power of the ultrasonic treatment is 100 W, and the time of the ultrasonic treatment is 10 min to 20 min.

4. The method according to claim 1, characterized in that: In step (1), the titanium alloy is thoroughly rinsed with distilled water for 3 to 5 times, and then dried with a hair dryer to obtain a deoiled titanium alloy.

5. The method according to claim 1, characterized in that: In step (2), the electrolyte solution includes 15 g / L sodium aluminate, 1 g / L sodium hydroxide, and 4 g / L carbonyl iron powder.

6. The method according to claim 1, characterized in that: In step (2), the stirring time is 10 to 30 minutes, and is only performed when the electrolyte is sodium aluminate and sodium hydroxide. After the stirring is completed, carbonyl iron powder is added for ultrasonication, and the ultrasonication time is 10 to 30 minutes.

7. The method according to claim 1, characterized in that: In step (3), the micro-arc oxidation treatment process adopts a constant voltage mode, and the micro-arc oxidation electrical parameters include: a forward duty cycle of 10% to 25%, a forward termination voltage of 250 to 350 V, a negative duty cycle of 10% to 25%, a negative termination voltage of 50 V, a current frequency of 400 Hz, a micro-arc oxidation reaction time of 10 to 40 min, and a temperature of 20 to 40° C.

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