CN101712102A - Bionic metal ultra-wetting trans-scale structure design method and preparation method - Google Patents

Abstract

The invention relates to the technical field of laser microprocessing, in particular to a method for obtaining a metal-based ultra-wetting surface by designing the trans-scale structure of a metal surface, preparing a laser microstructure on the metal surface and carrying out necessary ultra-wetting decoration to the metal surface. The method comprises the following steps: firstly, designing a macroscopical large-area superficial periodical mastoid structure which simulates a locus leaf surface; constructing a micronano periodical structure on the microstructure of the mastoid structure to obtain a macroscopical-micronano trans-scale geometric model; adjusting laser parameters and a laser scanning path according to geometric parameters acquired after the bionic metal ultra-wetting trans-scale structure is designed; scanning the plane first time; rotating a sample 90 degrees; and scanning the plane again with low-energy laser. The trans-scale microstructure approaches to the surface appearance of a natural organism, is easy to calculate and analyze a contact angle and has a simple and controllable preparation process.

Description

Bionic metal ultra-wetting trans-scale structure design method and preparation method

Technical field

The present invention relates to the laser micro-machining technology field, refer in particular to striding the preparation of yardstick structure Design, metal surface laser micro-structural, in case of necessity micro-structure surface is carried out super wetting modification and obtain the method for the super wetting surface of Metal Substrate the metal surface.Be specially adapted to the ultra-wetting trans-scale structural design and the preparation of metals such as steel, Ti and alloy thereof, Cu and alloy thereof, Ni and alloy thereof, can be used for the automatically cleaning of material surface, the application that liquid flows aspects such as drag reduction, biocompatibility.

Background technology

Super wetting surface comprises super hydrophobic surface and ultra-hydrophilic surface.Super hydrophobic surface is meant with the contact angle of water and tumbles the angle less than 10 ° surface greater than 150 °, and aspect such as keep a public place clean in the surface of, satellite antenna antifouling at material surface and radar, the inhibition of organism surface microorganism adhering, petroleum pipeline inwall drag reduction is widely used.Ultra-hydrophilic surface is meant contact angle less than 5 °, and the time of sprawling is less than 0.5 second, and aspect such as, automatically cleaning antifog at material surface, Bc raising has important use.

The factor that influences the material surface wettability mainly comprises the character of material itself and the pattern on surface.The computing formula of the apparent contact angle of micro-structure surface that proposes according to Wenzel and Cassie, if the contact angle of smooth surface high with 90 °, increase surface roughness and can increase its contact angle; On the contrary, if the contact angle of smooth surface is lower than 90 °, increases surface roughness and can reduce its contact angle, therefore, is one of effective ways of the super wetting surface of preparation at the surface preparation coarse structure.What existing studies show that, the various biological surfaces of occurring in nature had that micron combines with nanophase strides the yardstick structure, thisly strides that the single micro-structural of scale ratio is easier to reach super wetting state.Surface micro-structureization generally is applied to the super wetting surface preparation of Inorganic Non-metallic Materials and polymeric material.In recent years, prepare micro-structural at metal material surface and be used, as electrochemical deposition, electroless plating replacement deposition, chemical attack, the vapour deposition of plasma auxiliary heat, autoxidation, laser ablation etc. with the method that obtains super wetting metal surface.

Yet, aspect preparation, generally there is structural design and prepares the phenomenon that the result disconnects mutually in bionical design of striding scale micro-structure, only be confined to during design than regular texture, as structures such as column, grating, graininess, this class formation is easy to calculate contact angle, but have than big difference with the natural yardstick structure of striding, as Chinese patent " laser preparation method of metal base ultra-hydrophobicity micro-structure surface " (publication number CN101219506A); To stride the similar structure of scale micro-structure to nature often be non-regular texture and some is prepared, this class formation is difficult to geometric modeling, thereby be difficult to determine real wetting state by the method for supposing its wetting state, calculating its contact angle, comparison result of calculation and experimental result, as the paper " Patterned Superhydrophobic Metallic Surfaces " of Anne-Marie Kietzig etc.In addition, the yardstick structure of striding that micron order cone structure that they obtain and submicron order ripple struction combine forms by a lasing area scanning, it generally all is ripple struction, ripple struction is not broken into nutty structure, therefore different with the micron mastoid process structure and the nanoparticle structure of lotus leaf surface.

Summary of the invention

The purpose of this invention is to provide the bionical super wetting function surface structure Design method of yardstick of striding of a kind of realization, and adopt laser technology to prepare Metal Substrate and stride the scale micro-structure surface with super wetability.

The invention is characterized in the bionical geometrical model of striding scale micro-structure of design, can be used to calculate contact angle, and determine the real wetting state of micro-structure surface by comparative experiments result and result of calculation.

The invention process process is as follows:

(1) structural design: macroscopical wide area surface cycle mastoid process structure of the imitative lotus leaf surface of design, structure micro-nano periodic structure constitutes macroscopic view-micro-nano and strides the yardstick geometrical model on micro-structural;

(2) sample is prepared: metal material is polished and polishing deionized water, acetone ultrasonic cleaning respectively.

(3) femtosecond laser is handled: sample is placed high vacuum chamber, open laser instrument, carry out twice surface scan behind the adjustment relevant parameter and handle.

(4) sample cleaning: take out the sample of handling well, ultrasonic cleaning, and dry up.

(5) the super wetting functionalization in surface:, generally can directly obtain ultra-hydrophilic surface if material is a water wetted material; Material is a hydrophobic material, then can directly obtain super hydrophobic surface.For striding the yardstick ultra-hydrophilic surface, can carry out hydrophobization to its surface and handle the acquisition super hydrophobic surface, carry out finishing to reduce the surface energy as sample being placed in the vacuum drying oven with low-surface-energy material (as silane), can obtain super hydrophobic surface; For striding the yardstick super hydrophobic surface, then can carry out hydrophilicity-imparting treatment and obtain ultra-hydrophilic surface its surface, as sample surfaces come with the method for spraying water wetted material or ultra-hydrophilic surface.

According to the wetting theory of classics, the degree of roughness that increases material surface can change its wetting effect effectively.The super-drainage structure of considering the lotus leaf macro surface by large scale mastoid process structure with and the small scale grain structure on surface form stride the yardstick structure, therefore, the present invention is in structural design, the paraboloid of revolution that adopts imitative mastoid process is as large-scale structure, the base diameter d1 of the paraboloid of revolution, high H1, cycle are P1, cover small scale grain structure, the diameter d 2 of particle, cycle P2 on it.According to designed geometrical model, derive the apparent contact angle computing formula on this surface, determine suitable geometric parameter according to formula, to satisfy desirable super wetting surface structure.

Open laser instrument, according to the geometric parameter that obtains after the bionic metal ultra-wetting trans-scale structure is designed, adjust laser parameter, optical maser wavelength is 400nm or 800nm, burst length 130fs, frequency 1kHz, laser single-pulse energy is regulated with an attenuator, and scanning used single pulse energy weight range for the first time is 0.2～2.5mJ, and the laser beam vertical focusing is in sample surfaces, regulate spot size, spot diameter 50～200 μ m by the distance that changes sample and focus lamp.Laser beam scan path is made up of the parallel lines of some, the length of these straight lines and spacing and sweep speed can accurately be regulated by the two galvanometer systems of computer system control, to realize flat scanning, the distance between centers of tracks size of selecting will guarantee overlapped above the hot spot of half, and laser scanning speed is 0.8～1.5mm/s.After having carried out flat scanning, obtain micron order paraboloid of revolution shape raised structures, and its surface coverage submicron order periodic dimple structure.To carry out flat scanning one time with low-energy laser again behind the sample half-twist, then the ripple struction that obtains can be interrupted becomes submicron particles, can obtain the micron order paraboloid of revolution structure of surface coverage submicron particles.It is accurately essential to scan for the second time used energy, the single pulse energy value of laser is lower than the energy threshold that produces ripple struction in smooth material surface scanning, generally get 5～20 μ J, too smallly then ripple can not be interrupted, the excessive ripple that then ripple is scanned fully for the second time acquisition replaces, can only obtain and scan the first time the vertical ripple struction of ripple direction that obtains, therefore need obtain accurate energy value by repetition test.The vacuum of vacuum target chamber is by a mechanical pump and a molecular pump control, and vacuum can reach 1 * 10 ^-5Pa.The laser beam that regulates enters vacuum target chamber and focuses on sample surfaces through quartz glass, and the clean level on quartz glass surface is very big to the pattern influence of the micro-structural of preparation, therefore will be in laser treatment process cleaned at regular intervals.

Advantage of the present invention:

That designs strides scale micro-structure near the natural biology surface topography, and is easy to carry out the computational analysis of contact angle.Micro-structural selects the large scale Periodic Rotating parabolic and small scale periodicity grain structure combines strides scale micro-structure, mastoid process structure near lotus leaf surface, obtain desirable wettability structure according to the contact angle computing formula parameter of can optimizing structure, and compare with result of experiment, can accurately analyze the true wetting state of real surface.

Preparation process is simple, controlled.The acquisition of the super wetting surface of Metal Substrate is handled by twice laser treatment and super humidification and is formed the technology simple and fast.Parameters such as output power of laser, spot diameter, scanning pattern, sweep speed and vacuum are independent controlled, and the surface micro-structure of acquisition can accurately be controlled by regulating these parameters.

Description of drawings

The design and the preparation flow schematic diagram of Fig. 1 bionic metal based super hydrophobic micro-structure surface

Fig. 2 femtosecond laser parallel micromachining system schematic

The mastoid process of the imitative lotus leaf surface of Fig. 3 is striden yardstick geometrical model and wetting model

The stainless steel sample surfaces pattern SEM figure of Fig. 4 femtosecond laser preparation and drop are at the wetting state figure of sample surfaces

1 computer, 2 laser controllers, 3 fs-laser systems, 4 laser beams, 5 energy meters, 6 filter plates, 7 beam expanding lens, 8 speculums, 9 optical gates, 10 pairs of galvanometer systems, 11 focus lamps, 12 quartz glass, 13 vacuum target chambers, 14 sample platforms, 15 samples, 16 vacuum target chamber control cabinets

The specific embodiment

Fig. 1 is design and preparation method's schematic flow sheet on bionic metal superhydrophobic microstructure surface.At first carry out bionical microstructure appearance design, the biological surface pattern carries out geometric modeling, is simplified to the structure that is easy to the laser preparation, and designs the geometric parameter of optimization; Go out corresponding laser parameter according to the design of Structural Parameters of optimizing.Sample surfaces polishes and polishes; Surface after polishing usefulness deionized water and acetone are distinguished ultrasonic cleaning 30 minutes, dry up with the cold blowing blower fan; Sample is placed on the specimen holder of vacuum target chamber, target chamber is pumped into high vacuum; Laser parameter control laser instrument with designing carries out femtosecond laser parallel micromachining, uses earlier the high energy laser flat scanning, will carry out flat scanning one time with selected low-energy laser again behind the sample half-twist subsequently; With the sample acetone ultrasonic cleaning that laser treatment is crossed, remove the processing spittle and the impurity on surface; Sample is carried out silanization with silane reagent in vacuum oven handle.

Fig. 2 is the femtosecond laser parallel micromachining schematic diagram.The laser beam of femto-second laser output enters two galvanometer systems and is focused mirror focusing behind filter plate, beam expanding lens, enter vacuum target chamber through the laser beam that focuses on through quartz window, directly acts on the sample surfaces on the sample platform.Output power of laser is measured by the energy meter that is placed on before the filter plate, and the size of energy is controlled by laser controller, measures the back energy meter and is removed; The optical gate of control laser break-make, the scanning pattern of two galvanometer systems and sweep speed are by computer system control; Vacuum in the vacuum target chamber is controlled by the vacuum target chamber control cabinet.

Fig. 3 strides yardstick geometrical model and wetting model for the mastoid process of imitative lotus leaf surface.Figure (a) is a large scale paraboloid of revolution periodic structure, and figure (b) is a partial enlarged drawing shape, and there is drop wetting state model on its surface, and paraboloid of revolution base diameter is d1, highly is H1, and the cycle is P1.Figure (c) is the partial enlarged drawing on large scale paraboloid of revolution surface, is small scale hemisphere periodic structure, and figure (d) is the enlarged drawing of small-scale structure, and there is drop wetting state model on its surface, and periodically hemispheroidal diameter is d2, and the cycle is P2.

Super hydrophilic design: according to the formula of Wenzel theory in the wetting theory of classics $\cos {\mathrm{\θ}}_r^w=r\cos {\mathrm{\θ}}_e\text{,}$ Get the apparent contact angle θ of micro-structural in conjunction with geometrical condition _R1 ^wFor

$\cos {\mathrm{\&theta;}}_{r1}^W=(\frac{{\mathrm{\&pi;d}}_2^2}{{4P}_2^2}+1)(1-\frac{{\mathrm{\&pi;<figure-callout\; id="1"\; label="d"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">d</figure-callout>}}_1^2}{{4\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">P</figure-callout>}}_1^2}+\frac{{\mathrm{\&pi;<figure-callout\; id="1"\; label="d"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">d</figure-callout>}}_1^4}{96{\mathrm{<figure-callout\; id="1"\; label="H"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">H</figure-callout>}}_1^2{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">P</figure-callout>}}_1^2}[{(1+\frac{16{\mathrm{<figure-callout\; id="1"\; label="H"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">H</figure-callout>}}_1^2}{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">d</figure-callout>}}_1^2})}^{\frac{3}{2}}-1\left]\right)\cos {\mathrm{\&theta;}}_e---\left(1\right)$

θ wherein _eBe the intrinsic contact angle on smooth bionic metal surface, can directly measure on the bionic metal surface after polishing.Determine parameter d 1, H1, P1, d2, P2 according to computing formula, make contact angle be lower than 5 °, reach super hydrophily.

Super-hydrophobic design: according to the formula of Cassie theory in the wetting theory of classics ${\cos \mathrm{\&theta;}}_r^C=-1+f(\cos {\mathrm{\&theta;}}_e+1),$ Get the apparent contact angle θ of micro-structural in conjunction with geometrical condition _R1 ^cFor

${\cos \mathrm{\&theta;}}_{r1}^C=\frac{{{\mathrm{\&pi;<figure-callout\; id="1"\; label="d"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}^4{\tan }^2{\mathrm{\&theta;}}_{\mathrm{<figure-callout\; id="1"\; label="e"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">e</figure-callout>}1}}{64{{\mathrm{<figure-callout\; id="1"\; label="H"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">H</figure-callout>}}_1}^2{{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">P</figure-callout>}}_1}^2}(\cos {\mathrm{\&theta;}}_{\mathrm{<figure-callout\; id="1"\; label="e"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">e</figure-callout>}1}+1)-1---\left(2\right)$

θ wherein _E1Equal the apparent contact angle θ of the small scale micro-structural on paraboloid of revolution surface _R2 ^c, can obtain by following formula,

$\cos {\mathrm{\&theta;}}_{r2}^C=\frac{{\mathrm{\&pi;d}}_2^2{\sin }^2{\mathrm{\&theta;}}_{e2}}{{4P}_2^2}(\cos {\mathrm{\&theta;}}_{e2}+1)-1---\left(3\right)$

θ wherein _E2Be the intrinsic contact angle behind the smooth bionic metal surface silicon alkanisation, can directly measure on the bionic metal surface behind polishing and the silanization.Determine parameter d 1, H1, P1, d2, P2 according to computing formula, make contact angle surpass 150 °, reach super-hydrophobic state.

Fig. 4 strides yardstick periodic structure SEM figure and the drop wetting state figure at sample surfaces for 316L stainless steel sample surfaces.In process, the cycle P2 of submicron order semiglobe is only relevant with optical maser wavelength with the value of diameter d 2, changes the less P2=0.5 μ m that gets here, d2=0.35 μ m.Experiment records θ _E2=113 °, can calculate according to equation (3)

Also promptly obtain θ _E1=143 ° value.Suppose

Can calculate by equation (2) $\frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">d</figure-callout>}}_1^4}{{\mathrm{<figure-callout\; id="1"\; label="H"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">H</figure-callout>}}_1^2{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">P</figure-callout>}}_1^2}\&le;23.9.$ The value that satisfies this condition d1, H1, P1 has countless versions, the geometric properties of the micro-structural that processing is processed according to femtosecond laser, and the value of supposing d1, H1, P1 is the same order of magnitude, gets P1=20 μ m respectively, H1=20 μ m, d1=15 μ m, $\frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">d</figure-callout>}}_1^4}{{\mathrm{<figure-callout\; id="1"\; label="H"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">H</figure-callout>}}_1^2{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="H2009101835888E00012.png"\; state="\{\{state\}\}">P</figure-callout>}}_1^2}=0.32<23.9,$ Satisfy condition.Design the geometric parameter that obtains according to the 316L stainless steel is striden the yardstick structure, carry out surface scan behind adjustment laser parameter and the laser beam scan path and handle.The vacuum of selecting 3.5 * 10 ^-3Pa, face trace interval 30 μ m, sweep speed 1mm/s, the laser energy of face scanning for the first time is 600 μ J, the laser energy that scans for the second time behind the sample half-twist is 10 μ J.Figure (a) can find out that macroscopic periodically awl is the paraboloid of revolution, and figure (b) be a partial enlarged drawing, has shown that the large scale poppet surface arranging the micro-nano particle, and composition is striden the yardstick periodic structure.The structure that obtains is for periodically striding scale micro-structure, the about 16 μ m of base diameter of micron order awl, about 19 μ m of cycle, high about 18 μ m, all about 0.35 μ m of the diameter of submicron particles and height, about 0.5 μ m of cycle.Figure (c) and scheme (d) and be respectively drop at the wetting state figure of silanization micro-structural sample surfaces and silanization micro-structural sample surfaces not.Through measuring, this apparent contact angle of the striding the yardstick structure not contact angle during silanization is lower than 5 °, and the time of sprawling was ultra-hydrophilic surface less than 0.5 second; Contact angle is 166 ° behind the silanization, tumbles the angle and is lower than 4 °, is super hydrophobic surface.

For Ti and alloy thereof, it is 25 μ m that trace interval is set, and sweep speed is 0.8mm/s, and face scan laser energy is 600 μ J～800 μ J for the first time, for the second time the laser energy of scanning is 10～12 μ J, and what finally can obtain to be similar to 316L stainless steel sample strides the yardstick body structure surface; For copper and alloy thereof, above parameter is set to respectively: trace interval is 40 μ m, sweep speed is 1.5mm/s, face scan laser energy is 300 μ J～400 μ J for the first time, for the second time the laser energy of scanning is 7～9 μ J, and what finally can obtain to be similar to 316L stainless steel sample strides the yardstick body structure surface; For nickel metal and alloy thereof, above parameter is respectively: trace interval is 30 μ m, and sweep speed is 0.9mm/s, and face scan laser energy is 500 μ J～700 μ J for the first time, and the laser energy of scanning is 9～11 μ J for the second time.

Claims (11)

1. bionic metal ultra-wetting trans-scale structure design method is characterized in that: design macroscopical wide area surface cycle mastoid process structure of imitative lotus leaf surface, construct the micro-nano periodic structure on the structural micro-structural of mastoid process, obtain macroscopic view-micro-nano and stride the yardstick geometrical model.

2. the described bionic metal ultra-wetting trans-scale structure design method of claim 1, it is characterized in that: stride the yardstick structure as prototype with lotus leaf surface, adopt the large-scale structure of paraboloid of revolution simulation lotus leaf macro surface texture, the base diameter d1 of the paraboloid of revolution, high H1, cycle are P1; Adopt hemisphere simulation lotus leaf macro surface small-scale structure, hemispheroidal diameter d 2, cycle P2; According to designed geometrical model, derive the apparent contact angle computing formula on this surface, determine suitable geometric parameter according to formula, to satisfy desirable super wetting surface structure;

For super hydrophilic design: according to the formula of Wenzel theory in the wetting theory of classics $\cos {\mathrm{\&theta;}}_r^w=r\cos {\mathrm{\&theta;}}_e,$ Get the apparent contact angle θ of micro-structural in conjunction with geometrical condition _R1 ^wFor

$\cos {\mathrm{\&theta;}}_{r1}^W=(\frac{\mathrm{\&pi;}{d}_2^2}{4P_2^2}+1)(1-\frac{\mathrm{\&pi;}{d}_1^2}{4P_1^2}+\frac{\mathrm{\&pi;}{d}_1^4}{96H_1^2{P}_1^2}{[(1+\frac{16H_1^2}{d_1^2})}^{\frac{3}{2}}-1])\cos {\mathrm{\&theta;}}_e$

θ wherein _eBe the intrinsic contact angle on bionic metal surface, can directly measure the metal surface after polishing, determine parameter d 1, H1, P1, d2, P2, make contact angle be lower than 5 °, reach super hydrophily according to computing formula;

For super-hydrophobic design: according to the formula of Cassie theory in the wetting theory of classics $\cos {\mathrm{\&theta;}}_r^C=-1+f(\cos {\mathrm{\&theta;}}_e+1),$ Get the apparent contact angle θ of micro-structural in conjunction with geometrical condition _R1 ^cFor

$\cos {\mathrm{\&theta;}}_{r1}^C=\frac{\mathrm{\&pi;}{d_1}^4{\tan }^2{\mathrm{\&theta;}}_{e1}}{64{H_1}^2{P_1}^2}(\cos {\mathrm{\&theta;}}_{e1}+1)-1$

θ wherein _E1Equal the apparent contact angle θ of the small scale micro-structural on paraboloid of revolution surface _R2 ^c, θ _R2 ^cCan obtain by following formula,

$\cos {\mathrm{\&theta;}}_{r2}^C=\frac{\mathrm{\&pi;}{d}_2^2{\sin }^2{\mathrm{\&theta;}}_{e2}}{4P_2^2}(\cos {\mathrm{\&theta;}}_{e2}+1)-1$

θ wherein _E2Be the intrinsic contact angle behind the smooth bionic metal surface silicon alkanisation, can directly measure on the bionic metal surface behind polishing and the silanization.Determine parameter d 1, H1, P1, d2, P2 according to computing formula, make contact angle surpass 150 °, reach super-hydrophobic state.

3. the preparation method of bionic metal ultra-wetting trans-scale structure, comprise the sample preparation, femtosecond laser is handled and the sample cleaning, the concrete steps that femtosecond laser is handled are: sample is placed high vacuum chamber, open laser instrument, according to the geometric parameter that obtains after the bionic metal ultra-wetting trans-scale structure is designed, carry out the flat scanning processing first time after adjusting laser parameter and laser beam scan path, it is characterized in that: after having carried out flat scanning, to carry out flat scanning again one time with low-energy laser again behind the sample half-twist, the value that scans used single pulse energy for the second time is lower than the energy threshold that produces ripple struction in the smooth surface scanning of bionic metal.

4. the described preparation method of claim 3 is characterized in that: the optical maser wavelength that twice flat scanning handled is 400nm or 800nm, burst length 130fs, and frequency 1kHz, laser scanning speed are 0.8～1.5mm/s.

5. the described preparation method of claim 3 is characterized in that: scanning used single pulse energy weight range for the first time is 0.2～2.5mJ.

6. the described preparation method of claim 3 is characterized in that: the value that scans used single pulse energy for the second time is 5～20 μ J.

7. the described preparation method of claim 3 is characterized in that: it is overlapped that the distance between centers of tracks size of laser beam scan path will guarantee to surpass half hot spot.

8. the described preparation method of claim 3 is characterized in that: for stainless steel, trace interval 30 μ m, sweep speed 1mm/s, the laser energy of face scanning for the first time is 600 μ J, behind the sample half-twist for the second time the laser energy of scanning be 10 μ J.

9. the described preparation method of claim 3, it is characterized in that: for Ti and alloy thereof, trace interval is 25 μ m, and sweep speed is 0.8mm/s, and face scan laser energy is 600 μ J～800 μ J for the first time, and the laser energy of scanning is 10～12 μ J for the second time.

10. the described preparation method of claim 3, it is characterized in that: for copper and alloy thereof, trace interval is 40 μ m, and sweep speed is 1.5mm/s, and face scan laser energy is 300 μ J～400 μ J for the first time, and the laser energy of scanning is 7～9 μ J for the second time.

11. the described preparation method of claim 3, it is characterized in that: for nickel metal and alloy thereof, trace interval is 30 μ m, and sweep speed is 0.9mm/s, face scan laser energy is 500 μ J～700 μ J for the first time, and the laser energy of scanning is 9～11 μ J for the second time.

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