Recent Developments and Novel Applications of Laser Shock Peening: A Review

Abstract

Wear, corrosion, and fatigue are responsible for more than 80% of the failures of metallic materials. As most failures caused by wear, corrosion, and fatigue initiate from the material surface, surface integrity has a crucial impact on the overall performance of the materials. Surface integrity characteristics, including hardness, microstructure, morphology, roughness, and residual stress status, can significantly affect the wear and corrosion behavior. By improving hardness and introducing beneficial compressive residual stresses in the near-surface region, laser shock peening (LSP) can significantly improve the fatigue performance of metallic materials. In the LSP process, light from a high-energy pulsed laser penetrates through the transparent confinement media and irradiates the ablative coating, quickly heating the affected area to a high temperature and generating high-pressure plasma. The expansion of the plasma causes a shockwave that can plastically deform the target metals, resulting in work hardening and compressive residual stresses. Compared with shot peening (SP), LSP has the following advantages. 1) LSP can produce deeper layers of compressive residual stresses; 2) the process parameters in LSP can be precisely controlled; 3) the surface integrity of the parts after LSP is improved without the need for postprocessing; 4) LSP can be used to treat components with complex geometry; and 5) LSP has a high processing efficiency and makes for a clean working environment. Because LSP represents a new generation of surface strengthening technology that can replace SP, it has gained wide attention. Askar'yan and Moroz measured the pressures exerted by a high-intensity laser beam on the surface of a metal target [1] and found that this pressure is sufficient for steering space vehicles. However, the experiments were conducted under vacuum conditions to prevent dielectric breakdown, and such conditions are not practical for use in industry. [2] Anderholm at Sandia Laboratories irradiated an aluminum film covered in quartz with a laser beam and found that the presence of a transparent confinement layer can significantly increase the shock pressure. [3] Although this experiment was also conducted in vacuum, it proved that with the presence of a transparent confinement layer, a laser power density that does not cause dielectric breakdown in air can also generate a sufficiently large shock pressure. This observation is of great significance for the later industrial applications that involve laser-generated shockwaves.Fairand et al. at Battelle Memorial Institute changed the microstructure of 7075 aluminum alloy through short-pulse, laser-induced shockwaves with a high power density, and they found that after processing, the stress corrosion cracking (SCC) resistance and fatigue performance of the alloy improved. [4] This is a key event in the development of LSP; after this study, the National Science Foundation of the United States began to support the investigation of LSP. Clauer et al. [5] changed the intensity ...

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