Laser shock-hardening, physics and applications

Abstract

The laser shock-hardening is a rather recent process that is still under research in several laboratories. The shock wave generation uses the "confined regime" where the plasma expansion is delayed by using a laser transparent coating deposited at the target surface. Typical shock wave pressures of 50 kbars are then generated at laser intensities about 10 GW/cm2 with water confinement. The physics of this mechanism is discussed and the main limiting process for pressure generation, which are the breakdown mechanisms of the dielectric, is analysed. In a second part, the basic principles of shock wave propagation inside materials are recalled and allow the determination of the thickness of plastified material and of the residual stresses field generated inside the material. Also, the effect of different processing parameters such as the geometry of interaction, pulse repetition, and spatial separation are analysed. We will also present some applications devoted to the improvement of several properties for different materials such as their fatigue life or corrosion resistance. Comparisons of this treatment with a conventional surface treatment such as shot-peening will be also discussed. Finally, the key points for the achievement of an industrial laser processing machine will be defined.