CN111944989A

CN111944989A - Method for rapidly selecting area laser reinforcement

Info

Publication number: CN111944989A
Application number: CN202010923844.9A
Authority: CN
Inventors: 胡耀武; 程佳瑞; 刘胜; 叶畅
Original assignee: Wuhan University WHU
Current assignee: Wuhan University WHU
Priority date: 2020-09-04
Filing date: 2020-09-04
Publication date: 2020-11-17
Anticipated expiration: 2040-09-04
Also published as: CN111944989B

Abstract

The invention relates to the technical field of laser material modification, in particular to a method for rapidly selecting area laser reinforcement, which comprises the following steps: (1) manufacturing micro and nano structures on the surface of the transparent polymer; (2) coating a black absorbing layer on the micro-and nano-structures on the surface of the polymer; (3) scraping the redundant absorbing layer on the surface of the polymer to ensure that the absorbing layer material is only positioned in the grooves of the micro-structure and the nano-structure; (4) and (4) buckling the polymer obtained in the step (3) on the surface of the metal or metal composite material for laser shock strengthening. The workpiece is strengthened by the rapid selective area laser strengthening method, selective area strengthening can be performed on the surface of the metal or metal composite material, the strength and the ductility of the metal or metal composite material are improved simultaneously through the three-dimensional gradient microstructure effect, and the fatigue performance and the fracture toughness of the material can be enhanced.

Description

Method for rapidly selecting area laser reinforcement

Technical Field

The invention relates to the technical field of laser material modification, in particular to a method for rapidly selecting area laser reinforcement.

Background

Strength and toughness are two important properties for metal or metal composite applications, however, high strength materials tend to have poor ductility, while good toughness materials tend to have low strength, making it difficult to achieve both high strength and high toughness.

The existing strengthening methods for the workpiece, such as surface mechanical friction treatment, surface mechanical grinding treatment and the like, can remarkably improve the strength of the workpiece. It has been found through search that the prior US patent "Laser shock peening applications and methods" of patent application No. US20130180969a1 suggests the use of increasing or decreasing material temperature or the addition of active materials that interact with the energy field to enhance the Laser shock peening effect. The method has the defects that the ductility of the material is obviously reduced while the strength is improved by integrally processing the surface of the material, namely the surface of the processed material is easy to generate brittle cracks, and the method is not beneficial to the engineering application of workpieces. The present chinese patent application No. 201010278889.1, entitled apparatus and method for laser peening of hard and brittle materials, proposes a method for laser peening of brittle materials with high power continuous laser. Although the method can treat brittle and hard materials, the surface hardness of the treated materials is further improved, the ductility is further reduced, and sudden fracture and failure of the bearing member are easily caused. Therefore, the apparatus and method proposed in the prior patent are not suitable for laser peening fabrication that simultaneously improves the hardness and ductility of the material.

Disclosure of Invention

The invention aims to provide a method for rapidly selecting area laser strengthening, which can simultaneously increase the strength and the ductility of a metal or a metal composite material through a three-dimensional gradient microstructure effect and can enhance the fatigue property and the fracture toughness of the material.

The scheme adopted by the invention for realizing the purpose is as follows: a method of rapid selective area laser peening comprising the steps of:

(1) manufacturing micro and nano structures on the surface of the transparent polymer;

(2) coating a black absorbing layer on the micro-and nano-structures on the surface of the polymer;

(3) scraping the redundant absorbing layer on the surface of the polymer to ensure that the absorbing layer material is only positioned in the grooves of the micro-structure and the nano-structure;

(4) and (4) buckling the polymer obtained in the step (3) on the surface of the metal or metal composite material for laser shock strengthening.

Preferably, in the step (1), the micro-and nano-structures are fabricated on the surface of the transparent polymer by using any one of a soft lithography technique, a nano-imprinting technique, and a femtosecond laser technique.

Preferably, in the step (1), the transparent polymer is any one of polydimethylsiloxane, epoxy SU-8 resin and polymethyl methacrylate.

Preferably, in the step (2), the thickness of the absorption layer is 100nm-10 μm.

Preferably, in the step (2), the absorption layer is graphite or paint.

Preferably, in the step (4), the laser shock peening adopts a nanosecond laser, the laser pulse width is less than 1 microsecond, and the single pulse energy is higher than 10 mJ.

Preferably, in the step (4), the transparent solid or transparent liquid is pressed on the surface of the transparent polymer to serve as an impact restraint layer.

Preferably, the transparent solid is BK-7 glass or quartz glass with high impact resistance, and the transparent liquid is water or silicone oil.

The strengthening mechanism of the invention is as follows: the pulse laser ablates a graphite array filled in a groove of a micro or nano structure to generate plasma, the plasma expansion is restricted by an upper transparent polymer and an impact restriction layer to generate high-strength stress waves of a plurality of areas, so that a surface grain refinement and surface compression stress layer is generated in a surface selection area of the metal or metal composite material, gradient transition is generated between an amorphous phase of an impact reinforcement area and a crystalline phase of the non-reinforcement area, and therefore three-dimensional gradient microstructure distribution is generated, the effect of simultaneously enhancing the strength and the ductility of the material is achieved, and the fatigue performance and the fracture toughness of the material can be enhanced.

The invention has the following advantages and beneficial effects: the workpiece is strengthened by the rapid selective area laser strengthening method, selective area strengthening can be performed on the surface of the metal or metal composite material, the strength and the ductility of the metal or metal composite material are improved simultaneously through the three-dimensional gradient microstructure effect, and the fatigue performance and the fracture toughness of the material can be enhanced.

Drawings

FIG. 1 is a process flow diagram of the present invention;

FIG. 2 is a diagram illustrating the strengthening effect of the three-dimensional gradient microstructure according to the present invention.

In the figure, 101-transparent polymer, 102-absorbing layer, 103-metal or metal composite to be treated, 104-high impact resistant BK-7 glass, 105-pulsed laser, 106-stress wave, 107-impact strengthened amorphous region.

Detailed Description

The following examples are provided to further illustrate the present invention for better understanding, but the present invention is not limited to the following examples.

Example 1

As shown in fig. 1, a schematic process diagram of a rapid selective area laser strengthening method is shown, in which a rapid selective area laser strengthening treatment is performed on a pure copper plate: manufacturing a micro-nano structure on the surface of a Polydimethylsiloxane (PDMS) transparent polymer 101 by using a soft lithography technology or a nanoimprint technology; spraying 4-micrometer graphite 102 on the surface of the PDMS with the micro-nano structured surface; removing the redundant graphite coating by using a doctor blade; the PDMS with the grooves filled with graphite is reversely buckled on the surface of a metal or metal composite material 103 to be processed after the surface is polished, the surface is pressed by BK-7 glass 104 with high impact resistance, and then high-energy nanosecond laser 105 is irradiated to generate a plurality of high-pressure stress waves 106 in the material to carry out rapid selective area laser strengthening processing.

FIG. 2 is a diagram illustrating the strengthening effect of a three-dimensional gradient microstructure by a rapid selective area laser strengthening method. The strengthening mechanism of the invention is as follows: the pulse laser 105 ablates a graphite array filled in the groove to generate plasma, the expansion of the plasma is restricted by the upper transparent polymer 101 and the BK-7 glass 104 to generate high-strength stress waves 106 in a plurality of areas, so that surface grain refinement and surface compression stress layers are generated in selected areas of the surface of the workpiece, gradient transition is generated between an amorphous phase in an impact strengthening area and a crystalline phase in the non-strengthening area, three-dimensional gradient microstructure distribution is generated, the effect of simultaneously strengthening the strength and ductility of the material is achieved, and the fatigue performance and the fracture toughness of the material can be further enhanced.

The same technical effect can be achieved by replacing the BK-7 glass in example 1 with a flowing transparent liquid such as water or the like.

Example 2

Similar to fig. 1, the steel plate material is subjected to rapid selective area laser strengthening treatment: manufacturing a micro-nano structure on the surface of epoxy SU-8 resin or polymethyl methacrylate (PMMA) by using a femtosecond laser or soft lithography method; coating 10 micron graphite on SU-8 or PMMA with a micro-nano structured surface; removing the redundant graphite coating by using a doctor blade; SU-8 or PMMA with the groove filled with graphite is reversely buckled on the surface of a workpiece to be processed after the surface is polished, the workpiece is pressed by BK-7 glass with high impact resistance, and then high-energy nanosecond laser is irradiated to generate a plurality of high-pressure stress waves in the material to perform rapid selective area laser strengthening.

The reinforcing effect diagram of the three-dimensional gradient microstructure of the present embodiment is similar to that of fig. 2.

While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A method for rapid selective area laser peening, comprising the steps of:

2. The method of rapid selective area laser peening of claim 1, wherein: in the step (1), the micro-and nano-structures are manufactured on the surface of the transparent polymer by using any one of a soft lithography technology, a nano-imprinting technology and a femtosecond laser technology.

3. The method of rapid selective area laser peening of claim 1, wherein: in the step (1), the transparent polymer is any one of polydimethylsiloxane, epoxy SU-8 resin and polymethyl methacrylate.

4. The method of rapid selective area laser peening of claim 1, wherein: in the step (2), the thickness of the absorption layer is 100nm-10 μm.

5. The method of rapid selective area laser peening of claim 1, wherein: in the step (2), the absorption layer is graphite or paint.

6. The method of rapid selective area laser peening of claim 1, wherein: in the step (4), the laser shock peening adopts a nanosecond laser, the laser pulse width is less than 1 microsecond, and the single pulse energy is higher than 10 mJ.

7. The method of rapid selective area laser peening of claim 1, wherein: in the step (4), a transparent solid or a transparent liquid is pressed on the surface of the transparent polymer to be used as an impact restraint layer.

8. The method of rapid selective area laser peening of claim 7, wherein: the transparent solid is BK-7 glass or quartz glass with high impact resistance, and the transparent liquid is water or silicone oil.