阅读说明：本技术 一种面向大型结构件热源辅助激光冲击强化方法 (Auxiliary laser shock peening method for heat source of large structural part ) 是由 胡耀武 刘胜 张臣 张啸寒 赵哲 姜飞龙 谢琦 于 2021-06-09 设计创作，主要内容包括：本发明涉及一种面向大型结构件热源辅助激光冲击强化方法,其包括：向工件待强化区域喷涂吸收层材料,使得吸收层材料均匀覆盖待强化区域；开启低波段连续激光器,对工件待强化区域进行持续加热作业；向工件待强化区域喷射水约束层材料,使得水层均匀覆盖待强化区域；开启脉冲激光器,对工件待强化区域进行激光冲击强化作业；向工件强化区域喷射高压气流,去除残留水层；重复上述步骤,完成对工件不同区域的激光冲击强化。本发明中通过实时喷涂吸收层材料确保激光冲击作业过程中脉冲激光束与吸收层材料的有效作用,以避免传统方法因脉冲激光束与吸收层材料的过作用致使吸收层材料剥离而降低连续激光冲击作业的可靠性。(The invention relates to a heat source auxiliary laser shock peening method for a large structural member, which comprises the following steps: spraying an absorbing layer material on the region to be strengthened of the workpiece, so that the absorbing layer material uniformly covers the region to be strengthened; starting a low-waveband continuous laser, and continuously heating the region to be strengthened of the workpiece; spraying a water restraint layer material to the region to be strengthened of the workpiece, so that the region to be strengthened is uniformly covered by a water layer; starting a pulse laser, and carrying out laser shock strengthening operation on a region to be strengthened of the workpiece; jetting high-pressure airflow to the workpiece strengthening area to remove a residual water layer; and repeating the steps to finish the laser shock strengthening of different areas of the workpiece. The invention ensures the effective action of the pulse laser beam and the absorption layer material in the laser shock operation process by spraying the absorption layer material in real time, so as to avoid the phenomenon that the absorption layer material is stripped due to the over action of the pulse laser beam and the absorption layer material in the traditional method, thereby reducing the reliability of continuous laser shock operation.)

1. A heat source auxiliary laser shock peening method for a large structural part is characterized by comprising the following steps:

A) spraying an absorbing layer material on the region to be strengthened of the workpiece, so that the absorbing layer material uniformly covers the region to be strengthened;

B) starting a low-waveband continuous laser, and continuously heating the region to be strengthened of the workpiece;

C) spraying a water restraint layer to the region to be strengthened of the workpiece, so that a water layer uniformly covers the region to be strengthened;

D) starting a pulse laser, and carrying out laser shock strengthening operation on a region to be strengthened of the workpiece;

E) jetting high-pressure airflow to the workpiece strengthening area to remove a residual water layer;

F) and repeating the steps A) to E) to finish the laser shock strengthening of different areas of the workpiece.

2. A heat source-assisted laser shock peening method for large structures according to claim 1, wherein the material of the absorption layer in step a) is graphite, black paint or a mixture of two materials, and the thickness of the absorption layer is not less than 100 nm.

3. The method for auxiliary laser shock peening on large structural member as claimed in claim 1, wherein the laser wavelength of the low band continuous laser in step B) is 300-800nm, and the heating temperature of the low band continuous laser is higher than 200 ℃.

4. The heat source-assisted laser shock peening method for large scale structural members according to claim 1, wherein the thickness of the constraining layer in step C) is greater than 100 μm.

5. The heat source-assisted laser shock peening method for large structural members according to claim 1, wherein the pulsed laser in step D) is a pulsed laser generated by a millisecond, nanosecond, picosecond, femtosecond or attosecond laser, and the single pulse energy is not less than 1 mJ.

6. The heat source-assisted laser shock peening method for large structural members according to claim 1, wherein in step E), the high-pressure gas flow medium is one of compressed air, nitrogen, helium or argon, or a mixture of two or more of the above gases, and the pressure of the high-pressure gas flow is not less than 0.5 MPa.

Technical Field

The invention relates to the technical field of surface modification, in particular to a heat source auxiliary laser shock peening method for a large structural member.

Background

The large-scale complicated work piece of industry often possesses characteristics such as size is big, the quality is big and many irregular curved surfaces, and surface modification techniques such as traditional carburization, electroplating or hot spraying can't realize the accurate high-efficient strengthening operation in part of large-scale complicated work piece. Laser shock peening is a new technology for modifying a material to be strengthened by utilizing a plasma shock mechanical effect generated by inducing a high-power-density and low-pulse-width laser beam. Compared with the traditional surface strengthening technologies such as quenching, the laser shock strengthening technology can hardly generate heat effect on the surface of the material, has the advantages of cleanness, environmental protection, high operation efficiency, high controllability and the like, can generate a high residual compressive stress hardening layer on the surface layer of the material, and further remarkably improves the strength, hardness and tribology performance of the surface layer of the workpiece. Therefore, the laser shock peening process is considered to be an excellent surface modification technical method and is gradually applied to the fields of aerospace, marine ships, locomotive manufacturing and military industry.

It is worth noting that in the conventional laser shock operation under room temperature environment, the depth of the residual compressive stress hardening layer generated on the surface of the material is shallow, and the residual compressive stress is easy to release under the action of complex external environment and internal alternating load. Therefore, how to further enhance the strengthening effect of laser shock and obtain a structural member with excellent strength and plasticity becomes one of the technical bottlenecks that restrict further development and application of the laser shock technology in the technical field of material surface modification. The dynamic strain aging can increase the dislocation density generated by deformation, when the material is at the temperature of the dynamic strain aging, the diffusion of solute atoms is beneficial to dislocation nucleation, the pinning effect of the solute atoms on dislocations in the dynamic strain aging can cause work hardening, the stability of a dislocation structure is improved, and the laser-induced residual compressive stress is more stable. The dynamic precipitation refers to that a large amount of nano-scale precipitated phases are precipitated in the high-temperature plastic deformation process, dislocation generated by plastic deformation can have a positive effect on precipitation of the precipitated phases, and compared with static precipitation, the dynamic precipitation is more beneficial to processing and hardening. Therefore, in the laser shock operation process, the heating laser is introduced to perform heat source assisted laser shock strengthening, and the reliability of the laser shock operation is expected to be further improved through dynamic strain aging and dynamic precipitation.

At present, there are patent reports aiming at heat source assisted laser shock peening process, for example, chinese patent publication No. CN110578047A discloses a high temperature laser shock peening apparatus and method, a workpiece to be peened is clamped and placed in a protective cover by a fast clamping apparatus, and a heating platform is used to heat the whole workpiece, but there are also the following disadvantages: (1) the strengthening method provided by the patent is only suitable for small workpieces, has poor strengthening effect aiming at large complex structural parts, and cannot realize local precise strengthening of the large structural parts; (2) the device of the patent has a complex structure and high operation cost, and cannot be widely popularized and applied in the engineering field. The chinese patent publication No. CN101962710B discloses a device and method for laser shot peening strengthening of hard and brittle materials, wherein before laser shock operation, an absorption layer is uniformly preset on the surface of a workpiece, then high-power high-waveband continuous laser is used to perform auxiliary heating on the region of the workpiece to be strengthened, and high-power pulsed laser is synchronously used to perform shock strengthening on the region to be strengthened, but the following disadvantages exist: (1) the high-power high-waveband continuous heating laser has overlarge energy consumption; (2) after single shock operation of pulse laser, the absorption layer is excessively peeled off under the action of plasma pressure shock waves, and when laser shock strengthening operation of adjacent areas is performed, the strengthening effect of the laser shock operation is often affected due to the reduction of the coverage area of the absorption layer.

Disclosure of Invention

Aiming at the problems, the invention discloses a heat source auxiliary laser shock peening method for a large-scale structural member, and aims to solve the problems that local accurate peening of a large-scale complex structural member cannot be realized and the excessive action of plasma shock waves generated by pulse laser induction on a graphite absorption layer cannot be solved in the conventional heat source auxiliary laser shock peening technology.

The specific technical scheme is as follows:

a heat source auxiliary laser shock peening method for a large structural part is characterized by comprising the following steps:

A) spraying an absorbing layer material on the region to be strengthened of the workpiece, so that the absorbing layer material uniformly covers the region to be strengthened;

B) starting a low-waveband continuous laser, and continuously heating the region to be strengthened of the workpiece;

C) spraying a water restraint layer to the region to be strengthened of the workpiece, so that a water layer uniformly covers the region to be strengthened;

D) starting a pulse laser, and carrying out laser shock strengthening operation on a region to be strengthened of the workpiece;

E) jetting high-pressure airflow to the workpiece strengthening area to remove a residual water layer;

F) and repeating the steps A) to E) to finish the laser shock strengthening of different areas of the workpiece.

The method for reinforcing the heat source-assisted laser shock for the large structural member also has the characteristic that in the step A), the material of the absorption layer is graphite, black paint or a mixture of two materials, and the thickness of the absorption layer is not less than 100 nm.

The method for reinforcing the heat source-assisted laser shock for the large structural member also has the characteristics that in the step B), the laser wavelength of the low-band continuous laser is 300-800nm, and the heating temperature of the low-band continuous laser is higher than 200 ℃.

The method for the heat source-assisted laser shock peening of the large-scale structural part also has the characteristic that in the step C), the thickness of the constraint layer is more than 100 mu m.

The method for the heat source-assisted laser shock peening of the large-scale structural part also has the characteristic that in the step D), the pulse laser is pulse laser generated by a millisecond, nanosecond, picosecond, femtosecond or attosecond laser, and the single pulse energy is not less than 1 mJ.

The method for the heat source-assisted laser shock peening of the large structural member also has the characteristics that in the step E), the high-pressure airflow medium is one of compressed air, nitrogen, helium or argon, or a mixed gas of two or more gases; the pressure of the high-pressure airflow is not less than 0.5 MPa.

The strengthening mechanism of the invention is as follows:

the low-waveband laser beam emitted by the continuous heating laser accelerates the solidification of the material of the absorption layer and the material of the region to be strengthened of the workpiece in the continuous action process, and also raises the temperature of the material of the region to be strengthened of the workpiece to the dynamic strain aging temperature. The plasma shock wave propagating towards the thickness direction of the workpiece is induced while the pulse laser beam emitted by the pulse laser interacts with the material of the absorption layer, and the plasma shock wave generates shock pressure of GPa level under the constraint action of the water constraint layer, so that the material generates plastic deformation and generates a residual compressive stress hardening layer on the surface of the workpiece. After the single laser shock peening operation is finished, the residual water layer on the surface of the workpiece is removed by adopting high-pressure gas, so that the problem that the coating of an absorbing layer material is difficult and the continuous laser shock operation effect is influenced due to excessive residual water layers is avoided. By spraying the absorbing layer material in real time, the effective action of the pulse laser beam and the absorbing layer material in the laser shock operation process is ensured, and the problem of low reliability of continuous laser shock operation caused by stripping of the absorbing layer material due to the over-action of the pulse laser beam and the absorbing layer material in the traditional method, namely the preset absorbing layer material, is solved.

The dislocation density generated by deformation can be increased by dynamic strain aging, the diffusion of solute atoms is beneficial to dislocation nucleation when the material is at the temperature of dynamic strain aging, the pinning effect of the solute atoms on dislocations in dynamic strain aging can cause work hardening, the stability of a dislocation structure is improved, and the laser-induced residual compressive stress is more stable. And because a large amount of nano-scale precipitated phases are separated out in the high-temperature plastic deformation process, dislocation generated by plastic deformation can have a positive effect on the separation of the precipitated phases, and compared with static separation, dynamic separation is more beneficial to work hardening. Therefore, in the laser shock operation process, the heating laser is introduced to perform heat source assisted laser shock strengthening, and the reliability of the laser shock operation can be further improved through dynamic strain aging and dynamic precipitation.

The beneficial effect of above-mentioned scheme is:

1) by spraying the absorbing layer material in real time, the effective action of the pulse laser beam and the absorbing layer material in the laser shock operation process is ensured, and the problem of low reliability of continuous laser shock operation caused by stripping of the absorbing layer material due to the over-action of the pulse laser beam and the absorbing layer material in the preset absorbing layer material in the traditional method is solved;

2) by adopting the low-waveband continuous heating laser, the heating efficiency can be obviously improved under lower laser power, the curing rate of the material of the absorption layer can be accelerated, and the strength and the ductility of a laser shock-strengthened workpiece can be improved;

3) the invention has novel design thought, high feasibility and high operation efficiency, and is suitable for local precise laser shock peening of large-scale complex structural members.

Drawings

Fig. 1 is a schematic flow chart of heat source assisted laser shock peening provided in the present invention.

Fig. 2 is a schematic view of a heat source assisted laser shock peening apparatus provided in the present invention.

FIG. 3 is a graph showing tensile properties after impact reinforcement in example 1 of the present invention.

In the figure: a strengthened region 1; jet direction 2; a graphite spraying device 3; a water jet device 4; a pulse laser 5; a low-band continuous laser 6; an air flow injection device 7; connecting the support rod 8; a connecting pipe 9; an angle-adjusting steering controller 10; connecting the shaft 11.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

The present invention is further illustrated by the following examples, which are not to be construed as limiting the invention.

Example 1

As shown in fig. 1, a schematic diagram of a process of auxiliary laser shock peening for a heat source of a large structural member according to the present invention; fig. 2 is a schematic view of an auxiliary laser shock peening apparatus for a heat source of a large structural member according to the present invention. The heat source auxiliary laser shock peening treatment for the 7075 aluminum alloy pulse laser butt weld comprises the following steps:

A) connecting a connecting shaft 11 with an M-710iC six-axis automatic robot mechanical arm, adjusting an angle modulation steering controller 10, controlling the spatial positions of a connecting support rod 8 and a connecting pipe 9, enabling a jet flow direction 2 to face a 7075 aluminum alloy pulse laser butt weld reinforcement area 1, and spraying a graphite absorbing layer material (the thickness of graphite is about 5 microns) to the butt weld reinforcement area 1 by adopting a graphite spraying device 3, so that the graphite uniformly covers the butt weld reinforcement area 1;

B) a blue-light semiconductor continuous heating laser 6 (the wavelength of the laser is 450 +/-15 nm, the power of the laser is 80W, and the radius of a laser spot is 1.5mm) is selected to heat the butt weld reinforcement area 1 to 250 ℃;

C) a water layer (the thickness of the water layer is about 1.5mm) is sprayed to the butt weld reinforcement area 1 by adopting a water flow spraying device 4;

D) selecting a nanosecond pulse laser 5 (the laser wavelength is 1064nm, the pulse width is 7ns, the pulse frequency is 10Hz, the current is 10A, the voltage is 900V, the diameter of a laser spot is 1mm, the overlapping rate of the laser spot is 50%), overlapping the laser spot of the pulse laser 5 with the center of the laser spot of the blue semiconductor continuous heating laser 6 in the step C), and performing laser shock strengthening operation on the butt weld strengthening area 1 by using single pulse energy of 1J;

E) and (3) spraying high-pressure high-purity argon with the air pressure of about 0.6MPa to the butt weld reinforcement area 1 by adopting an air flow spraying device 7, and removing a residual water layer.

As shown in fig. 3, the tensile property curves of the sample directly subjected to laser shock peening by not heating and spraying graphite and the sample subjected to laser shock peening by heating and spraying graphite are compared in the present invention, and can be found in the following graph: the fracture elongation of the sample which is directly subjected to laser shock strengthening without heating and spraying graphite is only 27 percent, and the ultimate tensile strength is 33 MPa; the fracture elongation of the sample subjected to laser shock peening by heating and spraying the graphite layer is 41%, and the ultimate tensile strength is 44 MPa. Compared with the sample which is directly subjected to laser shock strengthening without heating and spraying graphite, the fracture elongation and the ultimate tensile strength of the sample which is subjected to laser shock strengthening by heating and spraying the graphite layer are respectively improved by 33 percent and 52 percent, so that the reliability of the structural member after the laser shock strengthening operation can be obviously improved by adopting the method provided by the invention.

Example 2

As shown in fig. 1, a schematic diagram of a process of auxiliary laser shock peening for a heat source of a large structural member according to the present invention; fig. 2 is a schematic view of an auxiliary laser shock peening apparatus for a heat source of a large structural member according to the present invention. The strengthening treatment of the superplastic forming blade made of the high-temperature titanium alloy IMI834 comprises the following steps:

A) connecting a connecting shaft 11 with an M-710iC six-axis automatic robot mechanical arm, adjusting an angle modulation steering controller 10, and controlling the spatial positions of a connecting support rod 8 and a connecting pipe 9 to enable a jet flow direction 2 to face a blade region to be strengthened 1; spraying a graphite absorbing layer material (the thickness of graphite is about 4 mu m) to the region 1 to be strengthened of the blade by using a graphite spraying device 3, so that the region 1 to be strengthened of the blade is uniformly covered by the graphite;

B) a blue-light semiconductor continuous heating laser 6 (the wavelength of the laser is 450 +/-15 nm, the power of the laser is 100W, and the radius of a laser spot is 1.5mm) is selected to heat the area 1 to be strengthened of the blade to 400 ℃;

C) a water layer (the thickness of the water layer is about 2mm) is sprayed to the area 1 to be strengthened of the blade by a water flow spraying device 4;

D) selecting a nanosecond pulse laser 5 (the laser wavelength is 1064nm, the pulse width is 10ns, the pulse frequency is 10Hz, the diameter of a laser spot is 3mm, the overlapping rate of the laser spot is 50%), overlapping the laser spot of the pulse laser 5 with the center of the laser spot of the blue semiconductor continuous heating laser 6 in the step B), and performing impact strengthening on the region 1 to be strengthened of the blade by using single pulse energy of 9J;

E) and (3) spraying compressed air with the air pressure of about 0.6MPa to the region 1 to be strengthened of the blade by adopting an air flow spraying device 7 to remove the residual water layer.

F) And repeating the steps A) to E) to finish the laser shock strengthening operation on different areas of the blade.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.