Titanium alloy surface strong corrosion resistance functionally graded coating and preparation method thereof

Abstract

The application discloses a kind of titanium alloy surface strong corrosion-resistant function gradient coating and preparation method thereof, steps: the ball valve to be sprayed is pretreated;After processing, ball valve is placed in rotating lathe fixed, and the programming of manipulator programmer equipped with plasma spraying gun is carried out;Select metal tantalum powder in the surface of ball valve to be sprayed Plasma Spraying Tantalum Bonding Layer;Carry out reverse powder feeding needle structure design, machining preparation work;Select reverse powder feeding needle to transport powder, adopt plasma spraying titanium dioxide powder on the surface of tantalum bonding layer to prepare titanium dioxide coating;The application introduces refractory metal tantalum as bonding layer, and uses reverse powder feeding needle to feed powder, with the characteristics of reasonable process, convenient operation, low cost, the prepared coating meets the requirements of high hardness, high bonding strength, high corrosion resistance, can significantly prolong the service life of titanium alloy ball valve.

Description

Technical Field

[0001] This invention belongs to the field of surface processing and modification technology, and relates to a functional gradient coating and its preparation method, particularly to a functional gradient coating with strong corrosion resistance on titanium alloy surface and its preparation method. Background Technology

[0002] Titanium alloy ball valves for nickel ore applications, under high-pressure acid leaching and pressurized oxidation conditions (as shown in Table 1-1), experience premature failure due to the combined effects of multiple factors, including high temperature, high pressure, high-concentration acidic solutions, and solid load-bearing requirements. Research indicates that ball valves without coatings have a service life of approximately 14 days. Therefore, to improve the reliability and service life of ball valves and reduce maintenance costs, research on high-performance protective coatings is urgently needed to meet the protection requirements of ball valves for high hardness, high bonding strength, and high corrosion resistance, thereby extending their service life.

[0003] Table 1-1 Specific parameters for high-pressure acid immersion service environment

[0004]

[0005] Currently, protective coating materials for ball valve surfaces mainly focus on Stellite 6 alloy coatings, WC-based coatings, and Cr3C2-NiCr coatings. However, due to the relatively poor corrosion resistance of these materials, they all have certain limitations in acidic environments. Titanium dioxide exhibits significant chemical stability and good corrosion resistance in acidic environments, meeting the corrosion protection requirements of coating materials.

[0006] Current research on titanium dioxide coatings still has the following shortcomings:

[0007] I. The density of titanium dioxide powder is 3.8~4.2 g / cm³. 3 Due to the low density of the powder, it is difficult to deliver the powder to the center of the plasma flame during the spraying process. The powder deposition efficiency is low, the melting state is poor, and the microstructure of the coating is not dense, which in turn affects the mechanical properties and corrosion resistance of the coating.

[0008] 2. For plasma spraying to prepare corrosion-resistant ceramic coatings, a no-undercoat design or nickel-chromium alloy or nickel-aluminum alloy is often chosen as the bonding layer.

[0009] For the former, the bonding strength between the ceramic coating and the ball valve is relatively weak, especially under extreme working conditions, the coating is prone to cracks and other damage, which can lead to coating peeling. For the latter, nickel-chromium alloy and nickel-aluminum alloy materials have relatively poor corrosion resistance, so it is necessary to find materials with relatively good corrosion resistance as the bonding layer.

[0010] Therefore, in order to meet the protection requirements of high hardness, high bonding strength and high corrosion resistance of titanium alloy ball valves for nickel ore, a coating composition / structure design was carried out to develop a functional gradient coating that meets the protection requirements of titanium alloy ball valves. Summary of the Invention

[0011] The primary technical problem to be solved by this invention is to provide a functionally graded coating with strong corrosion resistance on the surface of titanium alloys. This coating meets the requirements of high hardness, high bonding strength, and high corrosion resistance, and can significantly extend the service life of titanium alloy ball valves.

[0012] Another technical problem to be solved by the present invention is to provide a method for preparing a functionally graded coating with strong corrosion resistance on the surface of titanium alloy. The method has the characteristics of reasonable process and convenient operation. The prepared coating meets the requirements of high hardness, high bonding strength and high corrosion resistance, and can significantly extend the service life of titanium alloy ball valve.

[0013] The technical solution adopted by the present invention to solve the above-mentioned primary technical problem is: a functional gradient coating with strong corrosion resistance on the surface of titanium alloy, characterized in that: a tantalum bonding layer is first sprayed onto the surface of titanium alloy by plasma spraying, and then a titanium dioxide coating is sprayed by plasma spraying.

[0014] Preferably, the thickness of the tantalum adhesive layer is 50~90 μm.

[0015] Finally, the thickness of the titanium dioxide coating is at least 200 μm.

[0016] The technical solution adopted by this invention to solve the above-mentioned other technical problem is: a method for preparing a functionally graded coating with strong corrosion resistance on the surface of a titanium alloy, characterized by comprising the following steps:

[0017] 1) Clean and degrease the ball valve to be sprayed, roughen it with sandblasting, and perform a secondary cleaning treatment;

[0018] 2) Place the ball valve processed in step 1) on a rotary lathe and program the robot arm teach pendant for assembling the plasma spray gun;

[0019] 3) Select tantalum powder to plasma spray a tantalum bonding layer on the surface of the ball valve to be sprayed. Before spraying, preheat the ball valve to be sprayed. Spraying work is carried out after the temperature reaches 80~135℃.

[0020] 4) Conduct structural design and machining preparation of reverse powder feeding needles;

[0021] 5) Select the reverse powder feeding needle to deliver powder, and use plasma spraying of titanium dioxide powder to prepare a titanium dioxide coating on the surface of the tantalum bonding layer in step 3). Before spraying, preheat the tantalum bonding layer. Spraying is carried out after the temperature reaches 80~135℃.

[0022] As an improvement, the specific process of step 1) is as follows: before spraying, the ball valve is cleaned with gasoline and acetone to remove oil stains. Then, the pre-designed spraying fixture is assembled, and white corundum gravel is used for sandblasting roughening treatment. Finally, acetone solution is used to perform secondary cleaning of the sandblasted ball valve.

[0023] Furthermore, step 2) programming the robot teach pendant means: ensuring that the spraying distance between the robot and the spraying surface remains consistent during the spraying process, and maintaining a perpendicular relationship at all times, and setting different moving speeds of the spray gun according to the different arc chord lengths of the ball valve.

[0024] Furthermore, in step 3), the tantalum powder selected has a particle size distribution of 5~45μm, the tantalum coating thickness is 50~90μm, and the ball valve to be sprayed is preheated with plasma flame before spraying; the spraying temperature is monitored and controlled in real time using a temperature monitoring system and an adjustable flow rate liquid nitrogen cooling device to prevent the formation of thermal stress in the coating due to excessive temperature gradient, which would affect the coating's microstructure and properties.

[0025] The plasma spraying process is as follows: current of 500~550 A, argon gas flow rate of 30~80 NMPL, helium gas flow rate of 30~80 NMPL, spraying distance of 85~95 mm, preferably 90 mm, and powder feeding rate of 50~75 g / min.

[0026] Furthermore, step 4) of carrying out the reverse powder feeding needle structure design means that the inlet diameter R1 and the outlet diameter R2 of the powder feeding needle need to satisfy the relationship 1.2mm≤R1=R2≤2.0mm, where the inlet diameter R1 and the outlet diameter R2 are equal, and the inclination angle θ of the powder feeding tube should satisfy 105°≤θ≤155°.

[0027] Furthermore, the reverse powder feeding needle is made of steel.

[0028] Finally, in step 5), the particle size of the titanium dioxide powder is 5~45μm. A temperature monitoring system and an adjustable flow rate liquid nitrogen cooling device are used to monitor and control the spraying temperature in real time to prevent thermal stress from being generated in the coating due to excessive temperature and affecting the coating's microstructure and properties.

[0029] The thickness of the prepared titanium dioxide coating is at least 200 μm. The plasma spraying process is as follows: current of 500~550A, argon gas flow rate of 30~80 NMPL, helium gas flow rate of 30~80 NMPL, spraying distance of 85~95 mm, preferably 90 mm, and powder feeding rate of 40~65 g / min.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] 1. By introducing refractory metal tantalum as a bonding layer, a tantalum bonding layer is first prepared on the substrate surface, and then a titanium dioxide coating is prepared on the tantalum coating surface. This can improve the corrosion resistance and bonding strength of the coating system, ensure the stability of the coating in high-temperature and high-pressure service equipment, and extend the service life of the ball valve.

[0032] 2. Using a reverse powder feeding needle can deliver low-density, small-sized powder into the center of the flame, improve the melting state of the powder, promote the flattening of molten particles, and help improve the microstructure and properties of the coating.

[0033] This invention features a reasonable process, convenient operation, and low cost. The prepared coating meets the requirements of high hardness, high bonding strength, and high corrosion resistance, and can significantly extend the service life of titanium alloy ball valves. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the functional gradient coating on the surface of a ball valve according to an embodiment of the present invention;

[0035] Figure 2 This is a three-dimensional schematic diagram of a reverse powder feeding needle for plasma spraying according to an embodiment of the present invention;

[0036] Figure 3 This is a cross-sectional view of the reverse powder feeding needle;

[0037] Figure 4 This is a SEM image of the functional gradient coating on the surface of the ball valve according to an embodiment of the present invention;

[0038] Figure 5 Macroscopic view of the functional gradient coating on the surface of the ball valve and valve seat. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0040] Example 1

[0041] A method for preparing a highly corrosion-resistant functionally graded ceramic coating on a titanium alloy surface includes the following steps:

[0042] 1) The substrate is a TA12 titanium alloy ball valve. The surface of the cylindrical titanium alloy substrate with dimensions of φ25 mm × 6.5 mm is cleaned, degreased, sandblasted, and ultrasonically cleaned. The substrate is fixed on the spraying worktable, and a liquid nitrogen cooling pipe is introduced into the back of the substrate. The infrared temperature detection device spot is focused on the surface to be sprayed. The robot arm teach pendant equipped with the plasma spray gun is programmed to ensure that the spraying distance between the robot arm and the spraying surface remains consistent during the spraying process, and that the robot arm is always perpendicular to the surface. Different movement speeds of the spray gun are set according to the different arc chord lengths of the ball valve.

[0043] 2) Tantalum powder (particle size 5~45μm, spherical powder) for spraying is loaded into a powder feeding can. The titanium alloy substrate treated in step 1) is preheated using a plasma flame. When the infrared temperature detection system measures 85℃, plasma spraying to prepare the tantalum bonding layer begins, and the liquid nitrogen cooling pipeline is turned on. After five spray passes, a tantalum bonding layer with a thickness of 86 μm is obtained. The plasma spraying process parameters are: current 500A, argon gas flow rate 35 NMPL, helium gas flow rate 35 NMPL, spraying distance 90mm, powder feed rate 60g / min, and spraying speed 500mm / s.

[0044] 3) Conduct structural design and machining preparation of reverse powder feeding needles;

[0045] The reverse powder feeding needle is made of steel, which can withstand the wear and tear of powder for a long time, is economical, and can be reused.

[0046] Reverse powder feeding needle structure as follows Figure 2 , 3 As shown, the inlet diameter D1 and outlet diameter D2 of the reverse powder feeding needle need to satisfy the relationship 1.2mm ≤ D1=D2 ≤ 2.0mm, where the inlet diameter D1 and outlet diameter D2 are equal. This design ensures normal powder delivery. If D1<D2, airflow may become uneven. If D1>D2, powder blockage may occur in the powder feeding tube.

[0047] The tilt angle θ of the powder delivery pipe should satisfy 105°≤θ≤155°, which makes it easy to control and concentrate the airflow direction and avoid turbulence.

[0048] 4) Load the titanium dioxide powder (powder particle size 5~45μm, spherical nano-agglomerated sintered powder) for spraying into the powder feeding tank, select the reverse powder feeding needle to feed the powder, and use plasma flame to preheat the tantalum bonding layer obtained in step 2). When the infrared temperature detection system measures the temperature to be 100℃, start plasma spraying to prepare the titanium dioxide coating. The thickness of the prepared titanium dioxide coating is greater than or equal to 200μm.

[0049] The plasma spraying process parameters are as follows: current 500A, argon gas flow rate 30 NMPL, helium gas flow rate 30 NMPL, spraying distance 90mm, powder feed rate 43 g / min, and spraying speed 500mm / s.

[0050] The prepared ball valve coating, such as Figure 1 As shown in the figure. SEM image of the functional gradient coating on the ball valve surface. Figure 4 As shown.

[0051] Table 1 shows the porosity, bonding strength, and electrochemical corrosion data of the functionally graded coating prepared in Example 1, measured in a 1 mol / L H2SO4 solution.

[0052] Table 1. Coating porosity, bonding strength, electrochemical corrosion potential, and current

[0053]

[0054] The data above shows that the coating prepared in this embodiment meets the requirements of high hardness, high bonding strength, and high corrosion resistance.

[0055] After being tested and verified in actual working conditions, the titanium alloy ball valve with a highly corrosion-resistant functional gradient coating prepared by this process has a service life of about 1 year.

[0056] Example 2

[0057] A method for preparing a highly corrosion-resistant functionally graded ceramic coating on a titanium alloy surface includes the following steps:

[0058] 1) The substrate is made of TA12 titanium alloy. The surface of the cylindrical titanium alloy substrate with dimensions of φ25 mm × 6.5 mm is cleaned, degreased, sandblasted, and ultrasonically cleaned. The substrate is fixed on the spraying worktable, and a liquid nitrogen cooling pipe is introduced into the back of the substrate. The infrared temperature detection device spot is focused on the surface to be sprayed. The robot arm teaching pendant equipped with the plasma spray gun is programmed to ensure that the spraying distance between the robot arm and the spraying surface remains consistent during the spraying process and that the vertical relationship is maintained at all times. Different moving speeds of the spray gun are set according to the different arc chord lengths of the ball valve.

[0059] 2) Tantalum powder (particle size 15~45μm, irregular shape) for spraying is loaded into a powder feeding can. The titanium alloy substrate treated in step 1) is preheated using a plasma flame. When the infrared temperature detection system measures 85℃, plasma spraying to prepare the tantalum bonding layer begins. At this time, the liquid nitrogen cooling pipeline is turned on. The plasma spraying process parameters are: current 530A, argon gas flow rate 50 NMPL, helium gas flow rate 50 NMPL, spraying distance 90mm, powder feed rate 65 g / min, and spraying speed 550mm / s.

[0060] 3) Conduct structural design and machining preparation of reverse powder feeding needles;

[0061] The reverse powder feeding needle is made of steel, which can withstand the wear and tear of powder for a long time, is economical, and can be reused.

[0062] Reverse powder feeding needle structure as follows Figure 2 , 3As shown, the inlet diameter D1 and outlet diameter D2 of the reverse powder feeding needle need to satisfy the relationship 1.2mm ≤ D1=D2 ≤ 2.0mm, where the inlet diameter D1 and outlet diameter D2 are equal. This design ensures normal powder delivery. If D1<D2, airflow may become uneven. If D1>D2, powder blockage may occur in the powder feeding tube.

[0063] The tilt angle θ of the powder delivery pipe should satisfy 105°≤θ≤155°, which makes it easy to control and concentrate the airflow direction and avoid turbulence.

[0064] 4) Load the titanium dioxide powder (powder particle size 5~25μm, irregular shape) for spraying into the powder feeding tank, and preheat the tantalum bonding layer obtained in step 2) with plasma flame. When the infrared temperature detection system measures the temperature to be 100℃, start plasma spraying to prepare the titanium dioxide coating. The thickness of the prepared titanium dioxide coating is greater than or equal to 200μm.

[0065] The plasma spraying process parameters are as follows: current 530A, argon gas flow rate 50 NMPL, helium gas flow rate 50 NMPL, spraying distance 90mm, powder feed rate 40 g / min, and spraying speed 500mm / s.

[0066] The prepared ball valve coating, such as Figure 1 As shown in the figure. SEM image of the functional gradient coating on the ball valve surface. Figure 4 As shown.

[0067] Table 2 presents the porosity, bonding strength, and electrochemical corrosion data of the functionally graded coating in Example 2, measured in a 1 mol / L H2SO4 solution.

[0068] Table 2 Coating porosity, bonding strength, electrochemical corrosion potential, and current

[0069]

[0070] The data above shows that the coating prepared in this embodiment meets the requirements of high hardness, high bonding strength, and high corrosion resistance.

[0071] After testing and verification under actual working conditions, the titanium alloy ball valve with a highly corrosion-resistant functional gradient coating prepared in this embodiment has a service life of about 1 year.

[0072] Example 3

[0073] A method for preparing a highly corrosion-resistant functionally graded ceramic coating on a titanium alloy surface includes the following steps:

[0074] 1) The substrate is a TA12 titanium alloy ball valve. The surface of the cylindrical titanium alloy substrate with dimensions of φ25 mm × 6.5 mm is cleaned, degreased, sandblasted, and ultrasonically cleaned. The substrate is fixed on the spraying worktable, and a liquid nitrogen cooling pipe is introduced into the back of the substrate. The infrared temperature detection device spot is focused on the surface to be sprayed. The robot arm teaching pendant equipped with the plasma spray gun is programmed to ensure that the spraying distance between the robot arm and the spraying surface remains consistent during the spraying process and that the vertical relationship is maintained at all times. Different moving speeds of the spray gun are set according to different arc chord lengths of the ball valve.

[0075] 2) Tantalum powder (particle size 5~25μm, spherical powder) for spraying is loaded into a powder feeding container. The titanium alloy substrate treated in step 1) is preheated using a plasma flame. When the infrared temperature detection system measures 85℃, plasma spraying to prepare the tantalum bonding layer begins. At this time, the liquid nitrogen cooling pipeline is turned on. The plasma spraying process parameters are: current 550A, argon gas flow rate 70 NMPL, helium gas flow rate 70 NMPL, spraying distance 90mm, powder feed rate 65 g / min, and spraying speed 550mm / s.

[0076] 3) Conduct structural design and machining preparation of reverse powder feeding needles;

[0077] The reverse powder feeding needle is made of steel, which can withstand the wear and tear of powder for a long time, is economical, and can be reused.

[0078] Reverse powder feeding needle structure as follows Figure 2 , 3 As shown, the inlet diameter D1 and outlet diameter D2 of the reverse powder feeding needle need to satisfy the relationship 1.2mm ≤ D1=D2 ≤ 2.0mm, where the inlet diameter D1 and outlet diameter D2 are equal. This design ensures normal powder delivery. If D1<D2, airflow may become uneven. If D1>D2, powder blockage may occur in the powder feeding tube.

[0079] The tilt angle θ of the powder delivery pipe should satisfy 105°≤θ≤155°, which makes it easy to control and concentrate the airflow direction and avoid turbulence.

[0080] 4) Load the titanium dioxide powder (powder particle size 5~25μm, nano-agglomerated sintered powder) for spraying into the powder feeding tank, and preheat the tantalum bonding layer obtained in step 2) with plasma flame. When the infrared temperature detection system measures the temperature to be 100℃, start plasma spraying to prepare the titanium dioxide coating. The thickness of the prepared titanium dioxide coating is greater than or equal to 200μm.

[0081] The plasma spraying process parameters are as follows: current 550A, argon gas flow rate 70 NMPL, helium gas flow rate 70 NMPL, spraying distance 90mm, powder feed rate 40 g / min, and spraying speed 500mm / s.

[0082] The prepared ball valve coating, such as Figure 1 As shown in the figure. SEM image of the functional gradient coating on the ball valve surface. Figure 4 As shown.

[0083] Table 3 shows the porosity, bonding strength, and electrochemical corrosion data of the functionally graded coating prepared in Example 3, measured in 1 mol / L H2SO4 solution.

[0084] Table 3 Coating porosity, bonding strength, electrochemical corrosion potential, and current

[0085]

[0086] The data above shows that the coating prepared in this embodiment meets the requirements of high hardness, high bonding strength, and high corrosion resistance.

[0087] After testing and verification in actual working conditions, the titanium alloy ball valve equipped with the highly corrosion-resistant functional gradient coating of this embodiment has a service life of about 1 year.

[0088] The innovation of this invention lies in:

[0089] I. A reverse powder feeding needle was designed, characterized by its ability to deliver low-density powder to the center of a plasma flame, improving the powder's melting degree and deposition efficiency, which is beneficial for preparing dense coatings. This powder feeding needle is particularly suitable for conveying low-density, small-sized ceramic powders. It can deliver nano-agglomerated sintered powders with particle size distributions of 5~25μm or 5~45μm, as well as spherical and irregularly shaped powders, to the center of the plasma flame.

[0090] Second, refractory metal tantalum is introduced as a binder layer to replace traditional coating materials such as nickel-chromium alloys and nickel-aluminum alloys. Tantalum has a melting point as high as 2996℃ and possesses excellent high-temperature strength and corrosion resistance. Choosing tantalum as a binder layer can effectively isolate the metal substrate from corrosive media that penetrate into the ceramic coating. The design of the tantalum binder layer is beneficial to improving the bonding strength and corrosion resistance of the coating.

[0091] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A functionally graded coating with strong corrosion resistance on the surface of titanium alloy, characterized in that: A tantalum bonding layer is first plasma-sprayed onto the surface of the titanium alloy, followed by a titanium dioxide coating applied by plasma spraying.

2. The functionally graded coating with strong corrosion resistance on the titanium alloy surface according to claim 1, characterized in that: The thickness of the tantalum bonding layer is 50~90 μm.

3. The functionally graded coating with strong corrosion resistance on the titanium alloy surface according to claim 1, characterized in that: The thickness of the titanium dioxide coating is at least 200 μm.

4. A method for preparing a functionally graded coating with strong corrosion resistance on the surface of a titanium alloy, characterized in that: Includes the following steps: 1) Clean and degrease the ball valve to be sprayed, roughen it with sandblasting, and perform a secondary cleaning treatment; 2) Fix the ball valve processed in step 1) on a rotary lathe and program the robot arm teach pendant for assembling the plasma spray gun; 3) Select tantalum powder to plasma spray a tantalum bonding layer on the surface of the ball valve to be sprayed. Before spraying, preheat the ball valve to be sprayed. Spraying work is carried out after the temperature reaches 80~135℃. 4) Conduct structural design and machining preparation of reverse powder feeding needles; 5) Select the reverse powder feeding needle to deliver powder, and use plasma spraying of titanium dioxide powder to prepare a titanium dioxide coating on the surface of the tantalum bonding layer in step 3). Before spraying, preheat the tantalum bonding layer. Spraying is carried out after the temperature reaches 80~135℃.

5. The preparation method according to claim 4, characterized in that: The specific process of step 1) is as follows: before spraying, the ball valve is cleaned with gasoline and acetone to remove oil stains. Then, the pre-designed spraying fixture is assembled, and white corundum gravel is used for sandblasting roughening. Finally, acetone solution is used to perform a secondary cleaning of the sandblasted ball valve.

6. The preparation method according to claim 4, characterized in that: Step 2) Programming the robot teach pendant means ensuring that the spraying distance between the robot and the spraying surface remains consistent during the spraying process and that they are always in a perpendicular relationship, and setting different moving speeds of the spray gun according to the different arc chord lengths of the ball valve.

7. The preparation method according to claim 4, characterized in that: In step 3), the tantalum powder selected has a particle size distribution of 5~45μm, and the tantalum coating thickness is 50~90 μm. Before spraying, the ball valve to be sprayed is preheated using a plasma flame. The spraying temperature is monitored and controlled in real time using a temperature monitoring system and an adjustable flow rate liquid nitrogen cooling device. The plasma spraying process is as follows: current of 500~550 A, argon gas flow rate of 30~80 NMPL, helium gas flow rate of 30~80 NMPL, spraying distance of 85~95 mm, and powder feeding rate of 50~75 g / min.

8. The preparation method according to claim 4, characterized in that: Step 4) Designing the reverse powder feeding needle structure means that the inlet diameter R1 and outlet diameter R2 of the powder feeding needle need to satisfy the relationship 1.2mm≤R1=R2≤2.0mm, where the inlet diameter R1 and outlet diameter R2 are equal, and the inclination angle θ of the powder feeding tube should satisfy 105°≤θ≤155°.

9. The preparation method according to claim 4, characterized in that: The reverse powder feeding needle is made of steel.

10. The preparation method according to claim 4, characterized in that: In step 5), the particle size of the titanium dioxide powder is 5~45μm. The spraying temperature is monitored and controlled in real time using a temperature monitoring system and an adjustable flow rate liquid nitrogen cooling device. The thickness of the prepared titanium dioxide coating is at least 200μm. The plasma spraying process is as follows: current is 500~550A, argon gas flow rate is 30~80NMPL, helium gas flow rate is 30~80NMPL, spraying distance is 85~95mm, and powder feed rate is 40~65 g / min.

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