Effects of Laser Peening Parameters on Plastic Deformation in Aqueous Glycerol Solution as Plasma Confinement Layer

Laser peening is a surface treatment technique that can improve the properties of metallic materials. Installation of the plasma confinement layer with liquid plays an important role to obtain high magnitude shock wave pressure. In this study, the effects of laser peening parameters in glycerol solution as plasma confinement layer were investigated through hardness and residual stress measurements. The stainless steel, SUS316L, has been used as a target sample. The experiments were carried out by varying the concentration of glycerol solution. Laser peening treatment under a liquid confining medium is advantageous because a dual-impulse peening effect can be obtained by the shock wave pressure due to the confinement of laser-induced plasma and collapse of the laser-induced cavitation bubble. The impact from both shock wave pressures and dynamics of a laser-induced cavitation bubble have been evaluated to consider deeply the effects of laser peening parameters on the hardness and residual stress of laser-peened samples. Glycerol solution around 20 wt% in concentration was found to be desirable in any laser peening parameters to achieve efficient laser peening treatment.