Laser-shock processing of steel

The laser induced shock hardening of metal surfaces has several advantages over the conventional surface hardening methods. In order to improve the shock hardening process, investigation into the physical processes involved is necessary. In the present study, the modeling of the laser pulsed heating process is considered and the closed form solution for the surface temperature rise is obtained. The recoil pressure developed during the surface ablation is formulated and the elastic-plastic wave generation due to impact loading of the surface is analyzed. The surface temperature profile, the magnitude of the recoil pressure, and the depth of resulting plastic region inside the substrate are predicted for mild and stainless steel workpieces. The study is extended to include experimental investigation of laser-shock processing. Nd:YAG laser is used to ablate the steel surfaces. SEM, TEM, and EDS are carried out for metallurgical and morphological examinations of the laser ablated region. Microhardness measurement is carried out and the prediction of depth of plastic zone from the wave propagation analysis is validated. It is found that the recoil pressure in the order of 1GPa is developed at the surface. The dislocations are generated in the surface vicinity of the substrate after the laser ablation of the surface due to the impact loading of the surface by a recoil pressure. The plastic zone extends about 450 μm below the surface and the predictions well agreed with the experimental findings.