Method for improving laser surface strengthening effect by increasing roughness

Abstract

The application discloses a method for improving laser surface strengthening effect by increasing roughness, which comprises the following steps: according to the material to be processed and its mechanical properties, determining whether the laser impact process and the laser impact processing process require coating of an absorbing layer coating on the surface of the material to be processed; for the laser impact surface without the absorbing layer coating, the surface roughness interval is Ra0.01-Ra0.1; for the laser impact surface with the absorbing layer coating, the surface roughness of the material to be processed is not higher than Ra0.01, and the surface roughness of the absorbing layer coating is Ra0.05-Ra0.5; the surface of the material to be processed and the coating is pretreated to obtain a specified surface rough state; and the laser impact strengthening treatment is performed on the material to be processed by using the determined laser impact process condition. The surface state of the absorbing layer coating enables the high-energy laser to generate the laser shock wave pressure with the highest intensity on the material surface, and the surface state of the material to be processed enables the shock wave pressure to be maximized and vertically incident.

Description

Technical Field

[0001] This invention belongs to the field of high-energy laser surface strengthening technology, specifically relating to a method for improving the laser surface strengthening effect by varying the roughness. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Laser shock peening is a green material post-processing technology that achieves surface strengthening by inducing plasma shock waves with pulsed lasers and causing significant plastic deformation of the material surface. Laser parameters such as laser energy, pulse width, and beam size are currently the main aspects to be adjusted in laser shock surface strengthening processes. However, the precision and wide range of adjustment of laser parameters largely depend on the equipment conditions of high-performance lasers. Therefore, effectively controlling the surface strengthening effect of laser shock peening from the perspective of adjusting non-laser parameters has significant economic value and application implications.

[0004] Absorbing and constraining layers are crucial post-processing conditions for laser-shocked materials, significantly impacting surface strengthening. Technicians have achieved limited control over the laser-shock effect by adjusting the surface coating of the material. However, existing laser-shock post-processing techniques suffer from low laser reception and utilization rates. This low laser energy utilization limits the improvement in surface mechanical properties such as microhardness and residual stress in laser-shocked structural materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for improving the surface strengthening effect of laser by varying the surface roughness.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] A method for improving the surface strengthening effect of laser by varying the surface roughness includes the following steps:

[0008] Based on the material to be processed and its mechanical properties, determine whether the laser shock process and the laser shock processing require the application of an absorption layer coating on the surface of the material to be processed.

[0009] For laser-shocked surfaces without an absorption layer coating, the surface roughness range is Ra0.01 to Ra0.1;

[0010] For laser shock surfaces with an absorption layer coating, the surface roughness of the material to be processed should not exceed Ra0.01, and the surface roughness of the absorption layer coating should be Ra0.05 to Ra0.5.

[0011] Pre-treat the surface of the material to be processed and its coating to obtain a specified surface roughness.

[0012] The material to be processed can be subjected to laser shock strengthening treatment using the established laser shock process conditions.

[0013] In some embodiments, the high yield strength material to be processed is selected with low surface roughness.

[0014] Laser shock peening requires the surface of the material to be processed to have a high laser absorption rate, and the surface of the absorbing layer coating to have a high laser utilization rate. The surface condition of the absorbing layer coating enables the high-energy laser to generate the highest intensity laser shock wave pressure on the material surface, while the surface condition of the material to be processed maximizes the perpendicular incidence of the shock wave pressure.

[0015] The presence of rough surface micro-nano structures can improve light absorption rate. From the perspective of laser receiver rate, increasing the surface roughness of the material to be processed is beneficial to improving the surface strengthening effect. Smooth surfaces ensure that the laser beam is perpendicular to the incident state at any position. From the perspective of laser utilization rate, reducing the surface roughness of the material to be processed is beneficial to improving the surface strengthening effect. The rational utilization of the surface roughness of the material is of great significance to the determination of effective laser shock processes. By utilizing the process characteristics of laser shock materials and the need to coat the material surface with an absorption layer, prefabricating processing states with different surface roughnesses on the material surface and the surface of the coated absorption layer can simultaneously meet the requirements of high-intensity laser shock for both laser receiver rate and laser utilization rate. The surface roughness of the material should allow for a trade-off between laser reception and utilization.

[0016] In some embodiments, the high yield strength material to be processed has a strength of not less than 600 MPa to 1000 MPa, a surface roughness of Ra0.001 to Ra0.1, and a surface roughness of the absorbent coating layer of Ra0.05 to Ra0.5 (if any).

[0017] High yield strength materials require higher shock wave pressure to induce significant plastic deformation, and the achievement of high shock pressure can depend on the higher laser utilization rate induced by lower surface roughness.

[0018] In some embodiments, the absorption layer coating is prepared using pulsed laser deposition technology.

[0019] Preferably, the absorption layer coating is a dark coating with high light absorption efficiency prepared by pulsed laser deposition technology.

[0020] Preferably, the absorber coating acquires a set surface roughness during the laser deposition process.

[0021] Deposition technology allows for the preparation of surface coatings with a preset roughness by adjusting process parameters, while using black paint or black tape directly makes it difficult to quantitatively process the surface roughness of the material's surface coating.

[0022] This is to avoid excessive smoothness, which would reduce the laser reception rate, and excessive roughness, which would result in excessive laser energy consumption.

[0023] More preferably, the dark coating is a graphite coating or a material of the same material as the target material to be processed.

[0024] In the process of preparing a surface absorption layer using pulsed laser deposition, the laser deposition target is selected from the material of the component to be processed. Using a deposition absorption layer of the same material can avoid the introduction of foreign matter and impurities onto the surface of the material to be processed by laser shock.

[0025] More preferably, the method for preparing the absorption layer coating is pulsed laser deposition, that is, graphite or a material of the same material as the target material to be strengthened is selected as the target material for laser deposition. Under the photothermal effect of the pulsed laser, the target material is sputtered and deposited onto the surface of the material to be strengthened, forming a surface coating with a specific roughness.

[0026] In some embodiments, the method for pretreating the material to be processed and its coating surface is selected from mechanical grinding, mechanical polishing or chemical polishing.

[0027] Preferably, the surface roughness is measured using a surface roughness meter, a white light interferometer, or a laser co-concentration microscope.

[0028] In some embodiments, the laser shock process includes, but is not limited to, laser energy, pulse width, and beam size.

[0029] Preferably, when the yield strength of the material to be processed is high, a high laser power density is selected. Using a predetermined laser shock blasting process, the target material is subjected to laser shock blasting, ultimately achieving high-strength surface strengthening of the material to be processed.

[0030] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0031] 1. The technical method described in this invention eliminates the dependence of existing high-efficiency laser shock on high-performance lasers, and realizes high-efficiency laser shock surface processing of materials to be processed from the perspective of non-laser parameter adjustment, which has significant economic benefits and obvious application potential.

[0032] 2. This invention uses pulsed laser deposition to pretreat the surface of materials to be processed, based on laser shock surface strengthening. It belongs to a new technology for all-laser material surface treatment. High-energy laser technology is green and pollution-free. Attached Figure Description

[0033] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0034] Figure 1 The diagram shows a process flow diagram of a method for improving the laser surface strengthening effect by varying roughness, as proposed in this invention. Detailed Implementation

[0035] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0036] The present invention will be further described below with reference to the embodiments.

[0037] Example 1

[0038] The laser shock blasting application was determined to be a 304 stainless steel specimen with a yield strength of 210 MPa. The proposed laser shock blasting energy was 5 J, the pulse width was 18 ns, and the circular beam diameter was 2 mm. Surface strengthening was performed using an uncoated laser shock blasting process. Based on the material's mechanical properties, the preferred surface roughness was determined to be Ra 0.07. Mechanical grinding was then used to maintain the surface roughness at approximately Ra 0.07. Surface strengthening was performed under the determined laser shock blasting process conditions, and the residual stress on the material surface was measured to be approximately -180 MPa using an X-ray residual stress meter.

[0039] Example 2

[0040] The laser shock blasting application was determined to be an FGH97 high-temperature alloy specimen with a yield strength of 950 MPa. The proposed laser shock blasting energy was 7 J, the pulse width was 18 ns, and the circular beam diameter was 2 mm. Surface strengthening was performed using an uncoated laser shock blasting process. Based on the material's mechanical properties, the optimal surface roughness was determined to be Ra 0.03. Mechanical grinding and polishing were then used to maintain the surface roughness at approximately Ra 0.03. Surface strengthening was performed under the determined laser shock blasting process conditions, and the residual stress on the material surface was measured to be approximately -900 MPa using an X-ray residual stress meter.

[0041] Example 3

[0042] The laser shock blasting application was determined to be an FGH97 high-temperature alloy specimen with a yield strength of 950 MPa. The proposed laser shock blasting energy was 7 J, the pulse width was 18 ns, and the circular beam diameter was 2 mm. Surface strengthening was performed using an uncoated laser shock blasting process. Based on the material's mechanical properties, the optimal surface roughness was determined to be Ra 0.06. Mechanical grinding was then used to maintain the surface roughness at approximately Ra 0.06. Surface strengthening was performed under the determined laser shock blasting process conditions, and the residual stress on the material surface was measured to be approximately -860 MPa using an X-ray residual stress meter.

[0043] Example 4

[0044] The laser shock blasting application was determined to be a 304 stainless steel specimen with a yield strength of 210 MPa. The proposed laser shock blasting energy was 5 J, the pulse width was 18 ns, and the circular beam diameter was 2 mm. A coated laser shock blasting process was used for surface strengthening. The surface roughness of the material to be processed was determined to be no higher than Ra 0.01. Within the limits of the pulsed laser deposition equipment, the surface roughness of the deposited absorption layer coating was determined to be Ra 0.08. Based on the surface roughness requirements of the material and its absorption layer coating, the material to be processed was mechanically ground to obtain a surface roughness no higher than Ra 0.005. Pulsed laser deposition was then performed on its surface to obtain a deposited coating with a surface roughness of approximately Ra 0.08. Graphite was selected as the target material for the pulsed laser deposition. Surface strengthening was performed using the determined laser shock blasting process conditions. The residual stress on the material surface was measured to be approximately -200 MPa using an X-ray residual stress meter.

[0045] Example 5

[0046] The laser shock blasting application was determined to be an industrial pure iron sample block with a yield strength of 150 MPa. The proposed laser shock blasting energy was 5 J, the pulse width was 18 ns, and the circular beam diameter was 2.2 mm. A coated laser shock blasting process was used for surface strengthening. The surface roughness of the material to be processed was determined to be no higher than Ra 0.01. Under the conditions allowed by the pulsed laser deposition equipment, the surface roughness of the deposited absorption layer coating was determined to be Ra 0.08. Based on the surface roughness requirements of the material and its absorption layer coating, the material to be processed was mechanically ground to obtain a surface roughness no higher than Ra 0.005. Pulsed laser deposition was then performed on its surface to obtain a deposited coating with a surface roughness of approximately Ra 0.08. Pure iron was selected as the target material for pulsed laser deposition. Surface strengthening was performed using the determined laser shock blasting process conditions. The residual stress on the material surface was measured to be approximately -140 MPa using an X-ray residual stress meter.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving the surface strengthening effect of laser by varying the surface roughness, characterized in that: Includes the following steps: Based on the material to be processed and its mechanical properties, determine whether the laser shock process and the laser shock processing require the application of an absorption layer coating on the surface of the material to be processed. For laser-shocked surfaces without an absorption layer coating, the surface roughness range is Ra0.01~Ra0.1; For laser shock surfaces with an absorption layer coating, the surface roughness of the material to be processed should not exceed Ra0.01, and the surface roughness of the absorption layer coating should be Ra0.05~Ra0.

5. Pre-treat the surface of the material to be processed and its coating to obtain a specified surface roughness. The material to be processed can be subjected to laser shock strengthening treatment using the established laser shock process conditions.

2. The method for improving the laser surface strengthening effect by varying roughness according to claim 1, characterized in that: Materials with high yield strength should be selected with low surface roughness. The strength of the high yield strength material to be processed is not less than 600 MPa. For laser shock surfaces with an absorption layer coating, the surface roughness of the material to be processed is Ra0.001~Ra0.1, and the surface roughness of the absorption layer coating is Ra0.05~Ra0.

5.

3. The method for improving the laser surface strengthening effect by varying roughness according to claim 1, characterized in that: The absorption layer coating was prepared using pulsed laser deposition technology.

4. The method for improving the laser surface strengthening effect by varying roughness according to claim 3, characterized in that: The absorption layer coating is a dark coating with high light absorption efficiency prepared using pulsed laser deposition technology.

5. The method for improving laser surface strengthening effect by varying roughness according to claim 3, characterized in that: The absorption layer coating acquires a set surface roughness during the laser deposition process.

6. The method for improving the laser surface strengthening effect by varying roughness according to claim 4, characterized in that: The dark coating is a graphite coating or a material of the same material as the target material to be processed.

7. The method for improving the laser surface strengthening effect by varying roughness according to claim 1, characterized in that: Surface roughness is measured using a surface roughness meter, white light interferometer, or laser co-concentration microscope.

8. The method for improving the laser surface strengthening effect by varying roughness according to claim 1, characterized in that: The method for pretreatment of the material to be processed and its coating surface is selected from mechanical grinding, mechanical polishing or chemical polishing.

9. The method for improving the laser surface strengthening effect by varying roughness according to claim 1, characterized in that: The laser shock process parameters include laser energy, pulse width, and beam size.

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