Characteristics of surface layers formed on inconel 718 by laser shock peening with and without a protective coating

Coupons of a Ni base super alloy, Inconel alloy 718 (IN718) were laser shock peened with and without an ablative layer and resulting microstructure and residual stress state were studied. Laser shock peening without a protective overlay results in both mechanical and thermal loading of the material, leading to melting and re-solidification on the surface along with deformation due to laser induced shock wave. The surface shows presence of a non-uniform recast layer which increases the roughness of the surface and also results in a tensile state of residual stresses on surface. The recast layer has areas with modified chemistry and shows presence of nano particles deposited on top of the matrix. In this study, recast layer formed in Inconel alloy 718 (IN718) as a result of laser shock peening without protective overlay was characterized and compared with surface condition of a sample peened with a protective overlay. These results are presented and discussed in relation with those of previous studies.