A device and method for preparing a high-temperature-resistant ceramic coating on a titanium alloy surface by laser-assisted plasma sintering of nanoparticles

Abstract

The application discloses a device and a method for preparing a high-temperature-resistant ceramic coating on a titanium alloy surface through laser-assisted plasma sintering of nanoparticles; the device introduces one or more kinds of nanoparticles such as Al2O3, ZrO2 and CeO2 into an electrolyte column through a lateral nozzle, and the nanoparticles have good dispersibility, so that the loss of laser beams in the electrolyte column caused by a traditional nanoparticle introduction mode is avoided; in the device, laser energy directly acts on the nanoparticles, the nanoparticles are pre-melted or softened after absorbing the energy, and the nanoparticles are rapidly sintered into the coating under the action of a discharge plasma, so that the sintering efficiency of the nanoparticles in a selective area plasma electrolytic oxidation process is improved; the device accelerates the speed of the nanoparticles in participating in the formation of oxides, can improve the coating thickness and the surface micropore sealing effect, and can prepare a multifunctional composite ceramic coating by using nanoparticle solutions with different components and proportions, so that the heat resistance of the titanium alloy is improved.

Description

Technical Field

[0001] This invention discloses an apparatus and method for preparing high-temperature resistant ceramic coatings by laser-assisted plasma sintering of nanoparticles on the surface of titanium alloys. It involves laser surface modification and strengthening technology and selective plasma electrolytic oxidation technology. By using high-density laser energy to pre-melt and seal the micropores of nanoparticles through plasma electrolytic oxidation, the sintering efficiency of nanoparticles by discharge plasma is improved to prepare modified composite ceramic phase coatings, thereby enhancing the high-temperature service performance of titanium alloys. Background Technology

[0002] Titanium alloys are widely used in aerospace, marine, and medical fields due to their excellent mechanical properties, biocompatibility, corrosion resistance, light weight, and extremely high specific strength. However, when the operating temperature of titanium alloys exceeds 350℃, the TiO2 oxide film formed on its surface becomes loose and porous, unable to prevent the intrusion of oxygen, thus accelerating the oxidation rate. When the operating temperature exceeds 600℃, the high-temperature oxidation rate increases sharply, and the creep resistance is poor. When the temperature exceeds 700℃, the oxide film becomes brittle and easily peels off, seriously affecting the safety of titanium alloys in use. Therefore, titanium alloys are considered non-heat-resistant alloys with poor high-temperature oxidation resistance, limiting their further application as hot-end components. To address this, effective surface modification techniques can improve the service performance of titanium alloys at high temperatures.

[0003] Laser surface modification technology is a green and environmentally friendly non-contact processing technology. Lasers, with their advantages of concentrated energy, high energy density, high precision, and good controllability, are widely used for surface strengthening. By applying a laser beam to the workpiece surface, rapid heating alters the physical, chemical, and mechanical properties and microstructure of the surface material, including laser removal and laser additive manufacturing. For example, laser cladding heats and melts the cladding material and a thin layer on the workpiece surface together to form an alloyed coating. High-temperature beneficial elements such as Al, Nb, Si, Zr, and Y can be added to the cladding material to form a high-temperature oxidation-resistant coating.

[0004] Plasma electrolytic oxidation (PEO), as a green and environmentally friendly electrochemical surface coating modification technology, allows for flexible adjustment of electrical parameters and electrolyte combinations to prepare coatings with desired properties. This method involves in-situ growth of ceramic coatings, primarily composed of base metal oxides, on the surfaces of metallic metals such as Ti, Mg, and Al. The coating exhibits strong bonding strength with the substrate, good wear and corrosion resistance, and is simple to operate, enabling the processing of workpieces with complex shapes, thus attracting widespread research. PEO coatings have broad applications in high-temperature applications; the ceramic phase structure of the coating exhibits good high-temperature stability, and the absence of interdiffusion between coating elements at high temperatures allows for a significant preservation of the substrate's mechanical properties.

[0005] However, the porous structure of PEO-prepared coatings at high temperatures provides favorable channels for oxygen diffusion, which greatly weakens the long-term protective effect of the coating. Single plasma electrolytic oxidation cannot meet the higher thermal protection requirements of titanium alloys. Adding nanoparticles to the electrolyte can greatly improve film formation efficiency, repair surface defects, and seal micropores. However, nanoparticles are generally uncharged insulators, making it difficult to deposit onto the anode surface via electrophoresis, and they have poor dispersibility in the electrolyte, resulting in low efficiency in film formation. This invention proposes a method for laterally introducing nanoparticles and simultaneously sintering with laser, reducing energy loss during laser beam transmission in the liquid. It combines the advantages of laser surface modification technology and nanoparticle-modified plasma electrolytic oxidation, enabling nanoparticles to participate more efficiently in the oxidation reaction, improving coating thickness and density, and expanding the application of titanium alloys in high-temperature fields. Summary of the Invention

[0006] This invention provides an apparatus and method for preparing high-temperature resistant ceramic coatings on titanium alloy surfaces by laser-assisted plasma sintering of nanoparticles. By combining laser surface modification technology with nanoparticle-modified plasma electrolytic oxidation, a device for laterally introducing nanoparticles is designed, solving the problem of nanoparticles hindering laser transmission in the electrolyte. This allows for the preparation of a high-temperature resistant composite ceramic coating of Al2TiO5 / TiO2 / Al2O3 / ZrTiO4 on the surface of TC4 titanium alloy, providing a feasible solution for achieving thermal protection of titanium alloys.

[0007] The technical solution of the present invention is as follows:

[0008] An apparatus for preparing high-temperature resistant ceramic coatings by laser-assisted plasma sintering of nanoparticles on titanium alloy surfaces includes:

[0009] Ultrasonic disperser, nanoparticle container, filter, side nozzle, laser, jet cathode tube, pulse power supply, electrolytic cell, electrolyte collection device;

[0010] The nanoparticle container is used to contain a mixture of nanoparticles and electrolyte. The nanoparticle container is placed in an ultrasonic disperser and equipped with a stirrer to ensure that the nanoparticles are continuously and uniformly dispersed in the electrolyte and to promote the transport efficiency of the particles.

[0011] The side nozzle is fixedly connected to the jet cathode tube, which is perpendicular to the titanium alloy workpiece. The side nozzle is tilted at a certain angle relative to the jet cathode tube (preferably 30-60°) to ensure that the nanoparticle liquid column ejected by the side nozzle and the electrolyte column ejected by the jet cathode tube converge and merge at the center.

[0012] The side nozzle is fixed to the jet cathode tube and connected to the nanoparticle container through a pipe. A water pump and a speed control valve are installed on the pipe to regulate the flow rate. A filter is also installed on the liquid inlet pipe of the jet cathode tube to filter the nanoparticles and prevent them from entering the electrolyte column of the jet cathode tube and interfering with the transmission of the laser beam in the liquid.

[0013] The nanoparticle liquid column ejected from the side nozzle and the electrolyte column ejected from the jet cathode tube act on the surface of the workpiece and enter the electrolytic cell. They are collected by the electrolyte collection device connected to the bottom of the electrolytic cell and recycled back into the nanoparticle container under the action of the circulation pump.

[0014] An optical lens is provided at the upper end of the jet cathode tube, and a laser is provided above the optical lens. The laser beam emitted by the laser is coaxial with the electrolyte column ejected from the jet cathode tube and reaches the surface of the workpiece.

[0015] The titanium alloy workpiece and the jet cathode tube are respectively connected to the pulse power supply.

[0016] A method for preparing high-temperature resistant ceramic coatings by laser-assisted plasma sintering of nanoparticles on titanium alloy surfaces using the above-mentioned apparatus includes the following steps:

[0017] (1) Use sandpaper to grind the surface of the titanium alloy to remove the naturally formed oxide layer and reduce the surface roughness; then use a polishing machine to polish it to make the surface bright and achieve a mirror effect; then clean it with anhydrous ethanol, blow it dry and set it aside.

[0018] Titanium alloys, for example, TC4;

[0019] Specifically, the titanium alloy surface was polished using 80#, 240#, 500#, 800#, 1000#, 1500#, and 2000# sandpaper, respectively. The titanium alloy surface after polishing should have as few scratches as possible under an optical microscope to reduce the impact of surface condition differences on micro-arc oxidation discharge.

[0020] (2) Clamp the titanium alloy prepared in step (1) with the anode fixture of selective plasma electrolytic oxidation, operate the ABB robotic arm to adjust the position of the blue laser to ensure it is horizontal, turn on the water pump and the indicator light, make the indicator beam aligned with the center of the jet cathode tube jet liquid column, turn on the light, adjust the position of the laser beam to ensure that the laser is focused on the processing area covered by the liquid column, and turn off the light after successful debugging.

[0021] The preferred material for the jet cathode tube is stainless steel, with a diameter of 4mm;

[0022] In the selective plasma electrolytic oxidation process, the laser is focused onto the processing area covered by a liquid column of nanoparticles. The titanium alloy surface undergoes a plasma electrolytic oxidation reaction. The titanium alloy workpiece serves as the anode and is fixed by an anode fixture. The jet cathode tube serves as the cathode. Electrolyte delivered by a water pump flows out from the tubular cathode at a certain flow rate and contacts the anode titanium alloy workpiece to form a discharge circuit. The distance between the liquid column and the anode workpiece is called the electrode spacing. An electrolytic cell is installed on a CNC linear motion platform to receive and circulate the electrolyte. The anode is located above the electrolytic cell. The electrolytic cell moves linearly in the X / Y plane under the drive of the CNC platform. The entire ceramic coating is formed by overlapping each scanning pass.

[0023] (3) Adjust the position of the side nozzle so that the nanoparticle liquid column covers the plasma electrolytic oxidation reaction area, turn on the nanoparticle solution and electrolyte circulation pump, and turn on the oxidation power supply and blue laser at the same time. Under the combined action of laser energy and discharge plasma, the nanoparticles are sintered into the coating to prepare a ceramic coating.

[0024] The process parameters for plasma electrolytic oxidation are as follows: constant voltage mode, dual pulse, positive voltage 500-600V, negative voltage 100-300V, frequency 400-800Hz, duty cycle 10-30%.

[0025] The preferred laser is the KCTII-B500 blue semiconductor laser, with the following process parameters: spot size 1.87×1.87mm, working wavelength 450±nm, laser power 10~100W, and focal length 187mm.

[0026] The preferred overlap rate is 5-30%, the scanning speed is 1-4 mm / min, the electrode spacing is 8-12 mm, and the number of scanning passes is 1-2.

[0027] In the preferred nanoparticle liquid column ejected from the side nozzle, the concentration of nanoparticles is 1–10 g / L;

[0028] The nanoparticles are selected from one or more of Al2O3, ZrO2, and CeO2.

[0029] The electrolyte composition is as follows: NaAlO2 (main salt) 10-20 g / L, Na2HPO4·12H2O (additive) 5-10 g / L, NaOH (pH adjustment) 1-3 g / L, and deionized water as solvent;

[0030] The final ceramic coating includes multiphase composite coating structures such as Al2TiO5 / TiO2 / Al2O3 / ZrTiO4.

[0031] The technical principle of this invention is as follows:

[0032] Coatings prepared by micro-arc oxidation technology (plasma electrolytic oxidation) suffer from common problems such as surface micropores and microcracks. By adding nanoparticles to the electrolyte and sintering them into the coating under the action of plasma sparks, the coating is modified, pores are sealed, and defects are repaired, resulting in a multifunctional composite coating. However, traditional nanoparticle addition is only for immersion micro-arc oxidation, which suffers from problems such as nanoparticles being suspended in the electrolyte, poor dispersibility, low utilization rate, and difficulty in recycling. The focus and innovation of this invention lies in: using a high-energy laser beam to irradiate the nanoparticle solution, causing the nanoparticles to melt prematurely, which is more conducive to plasma spark sintering. Simultaneously, to avoid the electrolyte becoming turbid after the addition of nanoparticles, affecting laser beam energy loss, a lateral jet nozzle is designed to introduce the nanoparticles. The invention also includes recycling, ultrasonic dispersion, and a filtration system, which greatly improves the sintering efficiency of the nanoparticles, promotes the growth of the plasma electrolytic oxidation coating and the sealing of micropores, and enhances the thermal protection effect of the coating.

[0033] The present invention has the following beneficial effects and advantages:

[0034] (1) This invention combines the advantages of laser surface modification technology and nanoparticle modified plasma electrolytic oxidation technology to prepare a high-temperature resistant composite ceramic coating. It has a good sealing effect on the micropores of the coating and solves the defect problem of traditional plasma electrolytic oxidation coating in high-temperature protection. It can prepare Al2TiO5 / TiO2 / Al2O3 / ZrTiO4 multiphase composite structure according to different needs, providing a feasible solution for achieving better thermal protection performance of titanium alloys.

[0035] (2) Compared with the traditional nanoparticle composite plasma electrolytic oxidation processing method, the present invention adopts the side-spraying nanoparticle method to avoid the problem of laser propagation obstruction in the electrolyte column. The nanoparticles are highly dispersed and recycled and are easy to recover. The high energy density laser can accelerate the sintering and melting efficiency of nanoparticles, accelerate film formation efficiency, and improve coating thickness and density. Attached Figure Description

[0036] Figure 1 Schematic diagram of a laser-assisted plasma sintering device for nanoparticles.

[0037] Figure 2 : Mechanism diagram of laser-assisted plasma sintering of nanoparticles.

[0038] Figure 3 : The surface morphology of the coating prepared in Example 1.

[0039] Figure 1-2In the diagram, 1-ultrasonic disperser, 2-nanoparticle container, 3-stirrer, 4-water pump, 5-speed control valve, 6-filter, 7-side nozzle, 8-laser, 9-optical lens, 10-jet cathode tube, 11-laser beam, 12-pulse power supply, 13-molten nanoparticles, 14-workpiece, 15-electrolytic cell, 16-CNC linear motion platform, 17-electrolyte collection device, 18-micro-arc discharge plasma, 19-nanoparticles. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0041] In the following examples, the titanium alloy material is TC4, and the sample size is 20×14×2mm.

[0042] The KCTII-B500 blue semiconductor laser was used, with the following process parameters: spot size 1.87×1.87mm, working wavelength 450±nm, and focal length 187mm.

[0043] Electrolyte: Solutes are NaAlO2, Na2HPO4·12H2O, and NaOH; solvent is deionized water.

[0044] Nanoparticles: Al2O3, ZrO2, CeO2.

[0045] like Figure 1 As shown, an apparatus for preparing high-temperature resistant ceramic coatings by laser-assisted plasma sintering of nanoparticles on the surface of titanium alloys includes:

[0046] 1. Ultrasonic disperser; 2. Nanoparticle container; 6. Filter; 7. Side nozzle; 8. Laser; 10. Jet cathode tube; 12. Pulse power supply; 15. Electrolytic cell; 17. Electrolyte collection device.

[0047] The nanoparticle container 2 is used to contain the mixture of nanoparticles and electrolyte. The nanoparticle container 2 is placed in the ultrasonic disperser 1 and is equipped with a stirrer 3 to ensure that the nanoparticles can be continuously and uniformly dispersed in the electrolyte and to promote the transfer efficiency of the particles.

[0048] The side nozzle 7 is fixedly connected to the jet cathode tube 10. The jet cathode tube 10 is perpendicular to the titanium alloy workpiece 14. The side nozzle 7 is at a certain tilt angle relative to the jet cathode tube 10 to ensure that the nanoparticle liquid column ejected by the side nozzle 7 and the electrolyte column ejected by the jet cathode tube 10 converge and merge at the center.

[0049] The side nozzle 7 and the jet cathode tube 10 are connected to the nanoparticle container 2 through pipes. A water pump 4 and a speed regulating valve 5 are provided on the pipes to regulate the flow rate. A filter 6 is also provided on the liquid inlet pipe of the jet cathode tube 10 to filter the nanoparticles and prevent them from entering the electrolyte column of the jet cathode tube 10 and interfering with the transmission of the laser beam 11 in the liquid.

[0050] The nanoparticle liquid column ejected from the side nozzle 7 and the electrolyte column ejected from the jet cathode tube 10 enter the electrolytic cell 15, are collected by the electrolyte collection device 17, and are recycled back to the nanoparticle container 2 under the action of the circulation pump.

[0051] An optical lens 9 is provided at the upper end of the jet cathode tube 10, and a laser 8 is provided above the optical lens 9. The laser beam 11 emitted by the laser 8 is coaxial with the electrolyte column ejected from the jet cathode tube 10 and reaches the surface of the workpiece 14.

[0052] The titanium alloy workpiece 14 and the jet cathode tube 10 are respectively connected to the pulse power supply 12.

[0053] like Figure 2 As shown, this device prepares a multifunctional composite coating by adding different types of nanoparticles to the electrolyte through a side nozzle. Compared with the traditional method of adding nanoparticles, the side nozzle design will not affect the propagation of the laser beam. The high-density energy of the laser can make the nanoparticles melt in advance and accelerate sintering under the action of discharge plasma, filling and sealing the micropores on the plasma electrolytic oxidation surface, improving the film formation efficiency, and meeting the requirements of titanium alloy workpieces to serve in harsher environments, with excellent thermal protection performance.

[0054] like Figure 3 As shown, the surface morphology of the coating prepared in Example 1 was analyzed. The micro-arc oxidation coating has a small number of micropores and a small pore size. No obvious cracks were observed. Under the action of laser energy, some spherical oxides were generated on the coating surface. During the melting process, the defects on the coating surface may be covered, thus improving the density.

[0055] Example 1:

[0056] 1) Grind the surface of the titanium alloy using a polishing machine, clean it with alcohol, and air dry it to make the surface bright and smooth.

[0057] 2) Set the electrolyte ratio as follows: NaAlO2 15g / L, Na2HPO4·12H2O 10g / L, NaOH 3g / L, with deionized water as the solvent; adjust the electrode spacing to 9mm, the electrolyte temperature to below 40℃, and the electrolyte flow rate to 0.1m / s;

[0058] 3) Set the oxidation power supply parameters: constant voltage mode, dual pulse, positive voltage 600V, negative voltage 300V, frequency 500Hz, duty cycle ±30%;

[0059] 4) Set the overlap rate to 20%, scanning speed to 4 mm / min, and scanning pass to 1;

[0060] 5) Set the laser power to 80W and the focal length to 187mm;

[0061] 6) The nanoparticles are Al2O3 with a concentration of 4 g / L and the flow rate of the nanoparticle solution is 0.3 m / s;

[0062] Analysis of the prepared coating revealed that it had few micropores and cracks, and a dense structure.

[0063] Example 2:

[0064] 1) Grind the surface of the titanium alloy using a polishing machine, clean it with alcohol, and air dry it to make the surface bright and smooth.

[0065] 2) Set the electrolyte ratio as follows: NaAlO2 20g / L, Na2HPO4·12H2O 10g / L, NaOH 3g / L, with deionized water as the solvent; adjust the electrode spacing to 9mm, the electrolyte temperature to below 40℃, and the electrolyte flow rate to 0.1m / s;

[0066] 3) Set the oxidation power supply parameters: constant voltage mode, dual pulse, positive voltage 600V, negative voltage 300V, frequency 500Hz, duty cycle ±30%;

[0067] 4) Set the overlap rate to 20%, scanning speed to 4 mm / min, and scanning pass to 1;

[0068] 5) Set the laser power to 80W and the focal length to 187mm;

[0069] 6) The nanoparticles are Al2O3 with a concentration of 4 g / L and the flow rate of the nanoparticle solution is 0.3 m / s;

[0070] Analysis of the prepared coating revealed that it had few micropores and cracks, and a dense structure.

[0071] Example 3:

[0072] 1) Grind the surface of the titanium alloy using a polishing machine, clean it with alcohol, and air dry it to make the surface bright and smooth.

[0073] 2) Set the electrolyte ratio as follows: NaAlO2 20g / L, Na2HPO4·12H2O 10g / L, NaOH 3g / L, with deionized water as the solvent; adjust the electrode spacing to 9mm, the electrolyte temperature to below 40℃, and the electrolyte flow rate to 0.1m / s;

[0074] 3) Set the oxidation power supply parameters: constant voltage mode, dual pulse, positive voltage 600V, negative voltage 300V, frequency 500Hz, duty cycle ±30%;

[0075] 4) Set the overlap rate to 20%, scanning speed to 4 mm / min, and scanning pass to 1;

[0076] 5) Set the laser power to 80W and the focal length to 187mm;

[0077] 6) The nanoparticles are Al2O3 and ZrO2, both with a concentration of 4 g / L, and the flow rate of the nanoparticle solution is 0.3 m / s;

[0078] Analysis of the prepared coating revealed that it had few micropores and cracks, and a dense structure.

[0079] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. An apparatus for preparing high-temperature resistant ceramic coatings by laser-assisted plasma sintering of nanoparticles on titanium alloy surfaces, characterized in that, The device includes: Ultrasonic disperser, nanoparticle container, filter, side nozzle, laser, jet cathode tube, pulse power supply, electrolytic cell, electrolyte collection device; The nanoparticle container is used to contain a mixture of nanoparticles and electrolyte. The nanoparticle container is placed in an ultrasonic disperser and equipped with a stirrer to ensure that the nanoparticles are continuously and uniformly dispersed in the electrolyte and to promote the transport efficiency of the particles. The side nozzle is fixedly connected to the jet cathode tube, which is perpendicular to the titanium alloy workpiece. The side nozzle is tilted at an angle of 30 to 60 degrees relative to the jet cathode tube, ensuring that the nanoparticle liquid column ejected by the side nozzle and the electrolyte column ejected by the jet cathode tube converge and merge at the center. The side nozzle is fixed to the jet cathode tube and connected to the nanoparticle container through a pipe. A water pump and a speed control valve are installed on the pipe to regulate the flow rate. A filter is also installed on the liquid inlet pipe of the jet cathode tube to filter the nanoparticles and prevent them from entering the electrolyte column of the jet cathode tube and interfering with the transmission of the laser beam in the liquid. The nanoparticle liquid column ejected from the side nozzle and the electrolyte column ejected from the jet cathode tube act on the surface of the workpiece and enter the electrolytic cell. They are collected by the electrolyte collection device connected to the bottom of the electrolytic cell and recycled back into the nanoparticle container under the action of the circulation pump. An optical lens is provided at the upper end of the jet cathode tube, and a laser is provided above the optical lens. The laser beam emitted by the laser is coaxial with the electrolyte column ejected from the jet cathode tube and reaches the surface of the workpiece. The titanium alloy workpiece and the jet cathode tube are respectively connected to the pulse power supply.

2. A method for preparing high-temperature resistant ceramic coatings by laser-assisted plasma sintering nanoparticles on titanium alloy surfaces using the apparatus described in claim 1, characterized in that, Includes the following steps: (1) Use sandpaper to grind the surface of the titanium alloy to remove the naturally generated oxide layer and reduce the surface roughness; then use a polishing machine to polish it to make the surface bright and achieve a mirror effect; then clean it with anhydrous ethanol, blow it dry and set it aside. (2) Clamp the titanium alloy prepared in step (1) with the anode fixture of selective plasma electrolytic oxidation, operate the ABB robotic arm to adjust the position of the blue laser to ensure it is horizontal, turn on the water pump and the indicator light, make the indicator beam aligned with the center of the jet cathode tube jet liquid column, turn on the light, adjust the position of the laser beam to ensure that the laser is focused on the processing area covered by the liquid column, and turn off the light after successful debugging. (3) Adjust the position of the side nozzle so that the nanoparticle liquid column covers the plasma electrolytic oxidation reaction area, turn on the nanoparticle solution and electrolyte circulation pump, and turn on the oxidation power supply and blue laser at the same time. Under the combined action of laser energy and discharge plasma, the nanoparticles are sintered into the coating to prepare a ceramic coating. The nanoparticles are selected from one or more of Al2O3, ZrO2, and CeO2. The electrolyte composition is as follows: NaAlO2 10~20g / L, Na2HPO4·12H2O 5~10g / L, NaOH 1~3g / L, and deionized water as the solvent.

3. The method as described in claim 2, characterized in that, In step (1), the titanium alloy is TC4.

4. The method as described in claim 2, characterized in that, In step (2), the jet cathode tube is made of stainless steel and has a diameter of 4 mm.

5. The method as described in claim 2, characterized in that, In step (3), the process parameters for plasma electrolytic oxidation are as follows: constant voltage mode, dual pulse, positive voltage 500-600V, negative voltage 100-300V, frequency 400-800Hz, duty cycle 10-30%; The laser is a KCTII-B500 blue semiconductor laser with the following process parameters: spot size 1.87×1.87mm, working wavelength 450nm, laser power 10~100W, focal length 187mm; Overlap rate 5-30%, scanning speed 1-4 mm / min, electrode spacing 8-12 mm, scanning passes 1-2 times.

6. The method as described in claim 2, characterized in that, In step (3), the concentration of nanoparticles in the liquid column of nanoparticles ejected from the side nozzle is 1 to 10 g / L.

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