Method for processing three-dimensional fine structures on the surface of a metal by using a passivation solution to assist femtosecond laser

Abstract

The present invention discloses a method for passivation liquid-assisted femtosecond laser processing of three-dimensional fine structures on a metal surface, including: preprocessing of a metal sample; building a femtosecond laser processing system; fixing the preprocessed metal sample at the bottom of a container filled with passivation liquid, and loading a pre-designed hologram on a spatial light modulator; finding the surface of the metal sample within the field of view of a CCD camera, controlling the depth of the femtosecond laser entering the liquid by controlling the amount of passivation liquid in the container, and controlling the power density of the femtosecond laser in contact with the metal sample through an attenuator; after the femtosecond laser undergoes a coupling effect with the passivation liquid, it reaches the surface of the metal sample; directly writing and processing the metal sample; after the processing is completed, taking down the metal sample, ultrasonically cleaning it successively with ethanol and deionized water, and drying it. The passivation liquid can limit the generation of surface plasmon polaritons on the metal in the processing area, reduce the interference between the incident laser and the surface plasmon polaritons, and reduce the generation of two-dimensional periodic sub-wavelength structures.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal micro-nano processing. More specifically, the present invention relates to a method for processing three-dimensional fine structures on the metal surface by using a femtosecond laser assisted by a passivation solution. Background Art

[0002] The formation of micro-nano composite structures can endow excellent anti-reflection, drag reduction, coloring and other properties on the metal surface. Therefore, the preparation of micro-nano composite structures on the metal surface has become a research hotspot at home and abroad. In recent years, femtosecond lasers have been widely used in the field of micro-nano processing due to their characteristics such as ultrashort pulse width, ultra-high peak power and "cold processing". However, focusing the femtosecond laser spot to the nano / micron scale to prepare three-dimensional fine structures is extremely costly and has extremely low preparation efficiency; in an air environment, the interaction between the femtosecond laser and the metal material will generate ablation debris and irregular two-dimensional micro-nano periodic stripe structures on the material surface, making it difficult to achieve the processing of three-dimensional fine structures; in a pure liquid environment, due to the excitation of surface activity, the three-dimensional fine structures processed by the femtosecond laser will be quickly corroded; how to use femtosecond laser technology to quickly form stable three-dimensional fine structures on the metal surface is a major challenge in the field of metal micro-nano processing.

[0003] The patent "A Jet-Constrained Femtosecond Laser Ultra-Precision Machining System and Method" (Publication No.: CN109866028B) discloses a jet-constrained femtosecond laser ultra-precision machining system and method, including a B-axis workbench, a liquid tank, a laser jet coupling device, a plane mirror, a plano-convex lens, a first reflector, a second reflector, a bracket, and a C-axis chuck. During operation, under the control of an ultra-precision numerical control machine tool, the B-axis workbench and the C-axis chuck can rotate around the axis and move along the axis. The femtosecond laser is focused and coupled with the jet and reaches the workpiece surface. At the same time, the chemical solution undergoes micro-corrosion with the machined surface of the workpiece and removes defects such as the surface metamorphic layer. Subsequently, under the action of the water jet, debris and other impurities generated during the machining and chemical reaction processes are removed, improving the machining surface quality. Combining the five-axis linkage of the C-axis chuck and the B-axis workbench, three-dimensional structured micro-machining of workpieces with arbitrary shapes such as flat surfaces and free-form surfaces is completed. The patent "A Method for Preparing Superhydrophobic Surfaces by Combining Femtosecond Laser Direct Writing and Electroplating" (Publication No.: CN112872597B) relates to a method for preparing superhydrophobic surfaces by combining femtosecond laser direct writing and electroplating, belonging to the technical field of hydrophobic material preparation. It includes the following steps: (1) Laser surface machining is performed on a semiconductor or insulator substrate with a certain thickness metal layer on the surface by femtosecond laser to manufacture metal micro-line electrodes; (2) The prepared metal micro-line electrodes are used as electroplating cathodes and placed in an electrolyte solution for electroplating treatment, so that metal nanoparticles with adjustable morphology and size are electroplated on the surface of the metal micro-line electrodes, forming a flexible and adjustable metal micro-line-nanoparticle composite hydrophobic and superhydrophobic structure. The preparation method of the anti-icing functional structure provided by the patent "An Anti-icing Functional Structure and Its Preparation Method and Application" (Publication No.: CN112935571B) includes the following steps: A wedge-shaped micro-structure is prepared on the surface of the substrate to form a wedge-shaped micro-structure layer on the surface of the substrate; A nano-scale lattice is prepared on the surface of the wedge-shaped micro-structure layer to form a nano-scale lattice layer on the surface of the wedge-shaped micro-structure layer; The substrate with the nano-scale lattice structure layer on the surface is subjected to low surface energy treatment to form an anti-icing functional structure on the surface of the substrate. Although the above patents have successfully machined the three-dimensional structure on the material surface, there are problems such as low efficiency of the machining method and unstable properties of the generated structure. Therefore, inventing a method with higher efficiency and stable properties of the generated structure has become an urgent problem to be solved in the current field of metal micro-nano machining. Summary of the Invention

[0004] An object of the present invention is to solve at least the above problems and / or defects and provide at least the advantages described hereinafter.

[0005] To achieve these and other advantages in accordance with the present invention, there is provided a method for machining three-dimensional fine structures on the metal surface assisted by a passivation solution, including the following steps:

[0006] Step 1: Pretreat the metal sample. The surface of the metal sample is ultrasonically cleaned with ultrapure water, rinsed with anhydrous ethanol, and then dried with clean room-temperature air to obtain a clean metal sample surface.

[0007] Step 2: Set up the femtosecond laser processing system.

[0008] Step 3: Fix the metal sample pretreated in Step 1 at the bottom of a container filled with a passivation solution, and load a pre-designed hologram on the spatial light modulator. Locate the surface of the metal sample within the field of view of the CCD camera. Control the depth of the femtosecond laser entering the liquid by controlling the amount of the passivation solution in the container, and control the power density of the femtosecond laser in contact with the metal sample through an attenuator. After the femtosecond laser couples with the passivation solution, it reaches the surface of the metal sample. After determining the processing parameters of the metal sample, under computer control, the femtosecond laser performs direct writing processing on the metal sample through a scanning galvanometer or an electric control translation stage according to a pre-written processing program. After processing, remove the metal sample, ultrasonically clean it successively with ethanol and deionized water, and dry it to obtain a metal sample with a three-dimensional fine structure on its surface.

[0009] Preferably, in Step 3, the wavelength of the femtosecond laser source is 350 nm - 1064 nm, the repetition rate is 1 kHz, the pulse width is 35 fs - 260 fs, the power is 300 mW - 800 mW, the diameter of the femtosecond laser spot is 30 μm - 90 μm, the scanning line pitch is 30 μm - 90 μm, and the scanning rate is 1 mm / s.

[0010] The depth of the metal sample immersed in the passivation solution is 1 mm - 10 mm.

[0011] After the femtosecond laser couples with the passivation solution, it reaches the metal sample and is perpendicular to the tangent plane at any point on the surface of the metal sample.

[0012] Preferably, the material of the metal sample is iron and its alloys or stainless steel.

[0013] Preferably, the passivation solution is a transparent solution, including a nitrite solution and a molybdate solution, and further preferably a sodium nitrite solution with a mass fraction of 0.5%.

[0014] Preferably, in Step 1, the ultrasonic cleaning time of the surface of the metal sample in ultrapure water is 10 min - 20 min.

[0015] Preferably, in Step 2, the femtosecond laser processing system includes:

[0016] A femtosecond laser source, with an optical path transmission control system arranged outside its output port.

[0017] A real-time monitoring system, where the optical path transmission control system is located between the femtosecond laser light source and the real-time detection system;

[0018] A passivation liquid assisted processing system, which is located below the real-time monitoring system, and the container is placed on the passivation liquid assisted processing system.

[0019] Preferably, the optical path transmission control system includes:

[0020] An attenuation sheet, which is coaxially arranged with the output port of the femtosecond laser light source. A prism, a first lens and a second lens are coaxially arranged in sequence behind the attenuation sheet;

[0021] A first reflector, which is arranged behind the second lens;

[0022] A spatial light modulator, which is arranged above the first reflector. A diffraction grating is arranged above the spatial light modulator, and a second reflector is arranged below the diffraction grating;

[0023] A high-frequency optical shutter, which is arranged behind the second reflector. A beam splitter is arranged behind the high-frequency optical shutter. The beam splitter is located directly below the real-time monitoring system. A CCD is arranged directly above the beam splitter, and a scanning galvanometer is arranged directly below the beam splitter. The container is located below the scanning galvanometer.

[0024] Preferably, the passivation liquid assisted processing system is a stationary passivation liquid assisted processing system, which includes: a container containing passivation liquid, a metal sample is immersed in the passivation liquid, and the metal sample is fixed at the central position of the bottom of the container;

[0025] The container is fixedly connected directly above a three-dimensional electric control translation stage.

[0026] Preferably, the passivation liquid assisted processing system is a flowing passivation liquid assisted processing system, which includes:

[0027] A container containing passivation liquid, a liquid circulation device is arranged on the container, a metal sample is immersed in the passivation liquid, and the metal sample is fixed at the central position of the bottom of the container;

[0028] The container is fixedly connected to a three-dimensional electric control translation stage;

[0029] The liquid circulation device includes a circulation inlet of a control valve and a circulation outlet of the control valve, and both the circulation inlet and the circulation outlet are communicated with the container.

[0030] Preferably, the passivation liquid assisted processing system is a stirring passivation liquid assisted processing system, which includes:

[0031] A container containing a passivation liquid, wherein a liquid circulation device is provided on the container, a metal sample is immersed in the passivation liquid, and the metal sample is fixed at the center of the bottom of the container;

[0032] The container is fixed on a stirring platform, and the stirring platform is fixedly connected to a three-dimensional electric-controlled translation platform.

[0033] The present invention includes at least the following beneficial effects: the passivation liquid of the present invention can limit the generation of plasmons on the metal surface of the processing area, reduce the interference between the incident laser and the plasmons, and thus reduce the generation of two-dimensional periodic subwavelength structures; after the laser passes through the passivation liquid and interacts with the metal material, the material is instantly ionized and erupted, and the subsequent laser pulse interacts with the erupted particles, and a nano-submicron three-dimensional structure can be generated in one step within the range of the spot; the passivation liquid can take away part of the heat generated in the processing process, reduce the influence of the thermal effect on the processing process, and improve the surface quality and precision of the workpiece; a fresh surface is generated during the action of the femtosecond laser, and under the drive of the residual energy of the laser, the passivation liquid can quickly form a protective layer on the surface of the three-dimensional micro-nano structure, giving the metal surface stable and reliable properties; compared with processing in air, processing in the passivation liquid can effectively prevent processing debris from being deposited back on the sample surface, and reduce the pollution of the surface during the processing process.

[0034] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of the structure of a femtosecond laser processing system provided by the present invention;

[0036] Figure 2 Generate a scanning electron microscope image of a nanometer-micrometer three-dimensional structure in one step within the light spot range. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0038] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0039] Embodiment 1:

[0040] The method of passivation liquid assisted femtosecond laser processing of three-dimensional fine structures on metal surfaces in this embodiment includes the following steps:

[0041] Step 1: Use a stainless-steel sample for the metal sample. The surface of the stainless-steel sample is ultrasonically cleaned with ultrapure water for 10 minutes, rinsed with anhydrous ethanol, and then dried with clean room-temperature air to obtain a clean surface of the stainless-steel sample.

[0042] Step 2: Set up a femtosecond laser processing system. The structure of the femtosecond laser processing system is as Figure 1 shown, including:

[0043] A femtosecond laser light source 1, with an optical path transmission control system set outside its output port;

[0044] A real-time monitoring system, and the optical path transmission control system is located between the femtosecond laser light source and the real-time detection system;

[0045] A passivation liquid-assisted processing system, which is located below the real-time monitoring system, and the container is placed on the passivation liquid-assisted processing system.

[0046] Preferably, among them, the optical path transmission control system includes:

[0047] An attenuation sheet 2, which is coaxially arranged with the output port of the femtosecond laser light source 1. Behind the attenuation sheet 2, a prism 3, a first lens 4, and a second lens 5 are coaxially arranged in sequence;

[0048] A first reflecting mirror 6, which is arranged behind the second lens 5;

[0049] A spatial light modulator 7, which is arranged above the first reflecting mirror 5. Above the spatial light modulator 5, a diffraction grating 8 is arranged. Below the diffraction grating 8, a second reflecting mirror 9 is arranged;

[0050] A high-frequency light shutter 10, which is arranged behind the second reflecting mirror 9. Behind the high-frequency light shutter 10, a beam splitter 12 is arranged. The beam splitter 12 is located directly below the real-time monitoring system. Below the beam splitter 12, a scanning galvanometer 13 is arranged. Above the beam splitter 12, a CCD 11 is arranged. The container 14 is located below the scanning galvanometer 13, and the container is placed on a three-dimensional electric control translation stage 15.

[0051] A femtosecond laser with a pulse width of 120 fs, a wavelength of 800 nm, and a power of 500 mW is generated by a femtosecond laser light source. The femtosecond laser is expanded, modulated, compensated, and its optical path direction is changed through an optical path transmission control system composed of an attenuation sheet 2, a prism 3, a first lens 4, a second lens 5, a first mirror 6, a spatial light modulator 7, a diffraction grating 8, a second mirror 9, a high-frequency optical shutter 10, a beam splitter 12, and a scanning galvanometer 13. The femtosecond laser is attenuated by the attenuation sheet 2 to control the femtosecond laser power. The prism 3 expands the femtosecond laser. After expansion, it is focused by the first lens 4 and diffused by the second lens 5. Then, the femtosecond laser moving horizontally is reflected by the first mirror 6 into the spatial light modulator 7. The spatial light modulator 7 modulates the femtosecond laser. The modulated femtosecond laser is incident on the diffraction grating 8. The femtosecond laser is reflected again by the second mirror 9 to move horizontally. The horizontally moving femtosecond laser passes through the high-frequency optical shutter 10, which is used to control the on / off of the optical path. Finally, through the action of the beam splitter 12, a part of the femtosecond laser is incident upward into the CCD 11 to monitor and detect the shape and position of the laser oscillation spot in the resonant cavity in real time through the CCD 11. Another part of the femtosecond laser is incident downward onto the scanning galvanometer 13, and through the scanning galvanometer 13, the femtosecond laser is directed towards the container;

[0052] Step 3: Fix the stainless steel sample pretreated in Step 1 at the bottom of the container filled with the passivation solution, and load the pre-designed hologram on the spatial light modulator; find the surface of the stainless steel sample within the field of view of the CCD camera. Control the depth of the femtosecond laser entering the liquid by controlling the amount of the passivation solution in the container, and control the power density of the femtosecond laser in contact with the stainless steel sample through the attenuation sheet; control the depth of the stainless steel sample immersed in the passivation solution to be 5 mm. After the femtosecond laser spot with a diameter of 5 μm and a scanning line spacing of 50 μm and a scanning rate of 1 mm / s and a femtosecond laser repetition frequency of 1000 Hz interacts with the sodium nitrite solution with a mass fraction of 0.5%, it reaches the surface of the stainless steel sample. Under the control of the computer, the femtosecond laser performs direct writing processing on the stainless steel sample through the scanning galvanometer according to the pre-written processing program; after the processing is completed, take down the stainless steel sample, ultrasonically clean it with ethanol and deionized water for 10 min in sequence, and dry it to obtain a stainless steel sample with a three-dimensional fine structure on its surface. Its scanning electron microscope image is as Figure 2 shown.

[0053] The passivation solution-assisted processing system used in this embodiment is a flowing passivation solution-assisted processing system, and its structure includes:

[0054] A container containing the passivation solution, with a liquid circulation device arranged on the container. The stainless steel sample is immersed in the passivation solution, and the stainless steel sample is fixed at the central position of the bottom of the container;

[0055] The container is fixedly connected to a three-dimensional electric control translation stage;

[0056] The liquid circulation device includes a circulation flow inlet of the control valve and a circulation flow outlet of the control valve. Both the circulation flow inlet and the circulation flow outlet are communicated with the container.

[0057] The liquid circulation device controls the flow rate of the passivation liquid to be 10 mm / s. The passivation liquid reacts with the new surface after femtosecond laser processing to simultaneously form a three-dimensional structure and a protective layer on the surface of the stainless steel sample; the flowing passivation liquid is used for impurity removal and taking away part of the heat generated during the processing, so as to realize the ultra-precision processing of a stable three-dimensional micro-nano composite structure. The scale of the three-dimensional structure is 0.5 μm.

[0058] Example 2

[0059] The method for processing a three-dimensional fine structure on the metal surface by using a passivation liquid-assisted femtosecond laser in this example is the same as that in Example 1. The difference is that the passivation liquid-assisted processing system selected in this example is a static passivation liquid-assisted processing system, and its structure includes:

[0060] A container containing a passivation liquid, in which a metal sample is immersed, and the metal sample is fixed at the center position of the bottom of the container;

[0061] The container is fixedly connected directly above the three-dimensional electric control translation stage.

[0062] Example 3

[0063] The method for processing a three-dimensional fine structure on the metal surface by using a passivation liquid-assisted femtosecond laser in this example is the same as that in Example 1. The difference is that the passivation liquid-assisted processing system selected in this example is a stirred passivation liquid-assisted processing system, and its structure includes:

[0064] A container containing a passivation liquid, a liquid circulation device is arranged on the container, a metal sample is immersed in the passivation liquid, and the metal sample is fixed at the center position of the bottom of the container;

[0065] The container is fixed on a stirring table, and the stirring table is fixedly connected to the three-dimensional electric control translation stage.

[0066] Example 4

[0067] The difference between the method for processing a three-dimensional fine structure on the metal surface by using a passivation liquid-assisted femtosecond laser in this example and that in Example 1 is that the depth of the stainless steel sample immersed in the passivation liquid is 1 mm, the power of the femtosecond laser light source is 300 mW, the spot diameter is 30 μm, the scanning pitch is 30 μm, and the flow rate of the passivation liquid is 1 mm / s. The rest of the processes are the same as those in Example 1.

[0068] Example 5

[0069] The method for fabricating a three-dimensional fine structure on a metal surface assisted by a passivation solution in this embodiment is different from that in Embodiment 1 in that the depth of the stainless-steel sample immersed in the passivation solution is 10 mm, the power of the femtosecond laser source is 800 mW, the spot diameter is 90 μm, the scanning pitch is 90 μm, and the flow rate of the passivation solution is 20 mm / s. The remaining processes are the same as those in Embodiment 1.

[0070] The number of devices and the scale of processing described here are used to simplify the description of the present invention. Applications, modifications, and variations of the present invention will be apparent to those skilled in the art.

[0071] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the illustrated examples here.

Claims

1. A method for femtosecond laser processing of three-dimensional fine structures on a metal surface assisted by a passivation solution, characterized in that, It includes the following steps: Step 1: Pretreat the metal sample. The surface of the metal sample is ultrasonically cleaned with ultrapure water, rinsed with anhydrous ethanol, and then dried with clean room-temperature air to obtain a clean metal sample surface. Step 2: Set up a femtosecond laser processing system. Step 3: Fix the pretreated metal sample at the bottom of a container filled with a passivation solution. Load a pre-designed hologram on the spatial light modulator. The passivation solution is a sodium nitrite solution with a mass fraction of 0.5%. Locate the surface of the metal sample within the field of view of the CCD camera. Control the depth of the femtosecond laser entering the liquid by controlling the amount of the passivation solution in the container, and control the power density of the femtosecond laser in contact with the metal sample surface through an attenuator. After the femtosecond laser couples with the passivation solution, it reaches the surface of the metal sample. After determining the processing parameters of the metal sample, under computer control, the femtosecond laser performs direct writing processing on the metal sample through a scanning galvanometer or an electrically controlled translation stage according to a pre-written processing program. After processing, remove the metal sample, ultrasonically clean it successively with ethanol and deionized water, and dry it to obtain a metal sample with a three-dimensional fine structure on its surface. The femtosecond laser processing system includes: A femtosecond laser light source, with an optical path transmission control system arranged outside its output port. A real-time monitoring system, and the optical path transmission control system is located between the femtosecond laser light source and the real-time detection system. A passivation solution-assisted processing system, which is located below the real-time monitoring system, and the container is placed on the passivation solution-assisted processing system. The passivation solution-assisted processing system is a stirring passivation solution-assisted processing system. The optical path transmission control system includes: An attenuator, which is coaxially arranged with the output port of the femtosecond laser light source. A prism, a first lens, and a second lens are successively coaxially arranged behind the attenuator. A first reflector, which is arranged behind the second lens. The wavelength of the femtosecond laser light source is 350 nm - 1064 nm, the repetition frequency is 1 kHz, the pulse width is 35 fs - 260 fs, the power is 300 mW - 800 mW, the diameter of the femtosecond laser spot is 30 μm - 90 μm, the scanning line spacing is 30 μm - 90 μm, and the scanning rate is 1 mm / s.

2. The method for machining a three-dimensional fine structure on the metal surface by femtosecond laser assisted with a passivation solution according to claim 1, wherein The depth of the metal sample immersed in the passivation solution is 1 mm - 10 mm. After the femtosecond laser couples with the passivation solution, it reaches the metal sample and is perpendicular to the tangent plane at any point on the surface of the metal sample.

3. The method for machining a three-dimensional fine structure on a metal surface by using a femtosecond laser assisted with a passivation solution according to claim 1, characterized in that, The material of the metal sample is iron and its alloys or stainless steel.

4. The method for fabricating three-dimensional fine structures on a metal surface by femtosecond laser assisted with a passivation solution according to claim 1, wherein In Step 1, the ultrasonic cleaning time of the surface of the metal sample in ultrapure water is 10 min - 20 min.

5. The method for machining a three-dimensional fine structure on a metal surface by using a femtosecond laser assisted with a passivation solution according to claim 1, wherein The optical path transmission control system further includes: A spatial light modulator, which is arranged above the first reflector. A diffraction grating is arranged above the spatial light modulator, and a second reflector is arranged below the diffraction grating. A high-frequency shutter, which is arranged behind the second reflector. A beam splitter is arranged behind the high-frequency shutter. The beam splitter is located directly below the real-time monitoring system. A CCD is arranged directly above the beam splitter, and a scanning galvanometer is arranged directly below the beam splitter. The container is located below the scanning galvanometer.

6. The method for machining a three-dimensional fine structure on a metal surface by femtosecond laser assisted with a passivation solution according to claim 1, characterized in that The passivation liquid assisted processing system is a stationary passivation liquid assisted processing system, which includes: a container containing a passivation liquid, a metal sample immersed in the passivation liquid, and the metal sample is fixed at the center position of the bottom of the container; The container is fixedly connected directly above a three-dimensional electric control translation stage.

7. The method for femtosecond laser-assisted machining of three-dimensional fine structures on a metal surface using a passivation solution according to claim 1, wherein The passivation liquid assisted processing system is a flowing passivation liquid assisted processing system, which includes: a container containing a passivation liquid, a liquid circulation device is arranged on the container, a metal sample is immersed in the passivation liquid, and the metal sample is fixed at the center position of the bottom of the container; The container is fixedly connected to a three-dimensional electric control translation stage; The liquid circulation device includes a circulation flow inlet of a control valve and a circulation flow outlet of the control valve, and both the circulation flow inlet and the circulation flow outlet are communicated with the container.

8. The method for machining a three-dimensional fine structure on a metal surface by using a passivation solution to assist femtosecond laser according to claim 1, characterized in that The passivation liquid assisted processing system includes: a container containing a passivation liquid, a liquid circulation device is arranged on the container, a metal sample is immersed in the passivation liquid, and the metal sample is fixed at the center position of the bottom of the container; The container is fixed on a stirring table, and the stirring table is fixedly connected to a three-dimensional electric control translation stage.

Images