Plastic deformation of steel surface due to laser shock processing

Laser shock processing improves the properties of metallic surfaces, such as microhardness, through increased dislocation density. In the present study, laser shock processing of steel surfaces is considered. The recoil pressure developed across the vapour-solid interface is formulated and the temporal and spatial distributions of recoil pressure are computed. The stress wave generated owing to impacting force of recoil pressure and the plastic deformation in the substrate materials are computed. An experiment, in which an Nd:YAG laser is employed to irradiate the workpiece surface, is conducted to compare the predictions. Morphological and metallurgical changes in the laser-processed regions are examined using scanning electron microscopy and transmission electron microscopy. It is found that the hardness of surfaces improved considerably after the shock processing owing to enhanced dislocation sites in the surface region of the substrate material. The predicted recoil pressure agreed well with the results of previous formulations. The prediction of the depth of plastic region agrees well with the experimental results.