Effect of control of plasma confinement layer on laser peening

Effects of control of plasma confinement layer on laser peening have been studied. The plasma confinement layer for the laser peening is usually used the transparent medium to the laser wavelength, such as a glass and water. The confinement ability depends on the acoustic impedance of the medium. In this study, the acoustic impedance of the water has been controlled by dissolving sodium chloride (NaCl). Second harmonic of Nd: YAG laser having the pulse duration of 4 ns has been used for the laser peening experiments. Commercial SUS316L stainless steel has been adopted as a sample. The samples were investigated under nanosecond laser shock loading in plasma confined by aqueous sodium chloride solution. Vickers hardness test and X-ray diffraction method are used to probe work hardening and residual stress due to plastic deformation induced by laser peening. Through hardness and residual stress measurements, it is found that optimal concentration of the sodium chloride solution has been existed for the laser peening.