Multispot laser peening was conducted on austenitic stainless steel (SUS316L) using a Nd:YAG laser as the laser source to generate a high-intensity pulse ranging from 0.5–4 GW/cm2. A liquid-crystal-on-silicon spatial light modulator (LCOS-SLM) was used for laser division to create multiple spots on the target. Multiple laser pulses irradiating a metal surface simultaneously induce multiple shock waves. This approach leads to a thicker plastically deformed layer compared with laser-induced shock waves produced by a single pulse. The laser peening performance was evaluated by measuring the magnitude of the compressive residual stress, hardness difference, and magnitude of the laser-induced shock wave. The laser intensity and laser irradiation patterns were adapted as the laser peening parameters throughout the experiment.
Laser peening is a surface-enhancement technique that uses a high intensity of several gigawatts for the cold working of metal samples. The most notable feature of this technique is its effective treatment of the depths of metal samples. A transparent coating, known as a plasma confinement layer, is typically used in laser peening to suppress the expansion of the plasma away from the metal surface. The ability to confine the plasma significantly affects the effectiveness of laser peening. Water is commonly used as a plasma confinement layer due to its transparency, cost-effectiveness, ease of handling, and its ability to conform to the shape of metal as a liquid. However, in high-vacuum environments, only solid-state media can be used as plasma confinement layers. In this study, laser peening was performed in a high-vacuum environment using silicone rubber (polydimethylsiloxane) as the plasma confinement layer. It is softer and conforms to the shape of metal in a vacuum environment. Through experiments, the appropriate process window for laser irradiation was explored by varying the intensity and number of laser shots.
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