Laser shock processing of materials, physical processes involved and examples of applications

Laser shock processing (LSP) consists of irradiating a metallic; target with a short (about 20 ns) and intense (>10(13)W m(-2)) laser light in order to generate, through a high pressure surface plasma (>1 GPa), a plastic deformation and a surface strengthening within materials. This paper initially reviews the physical processes involved in the analytical modeling of the generation pressure mechanism in a confined plasma regime. Limiting factors such as the dielectric breakdown in the confining medium are also discussed together with current research directions aimed at improving the laser-material coupling such as using short rise time pulses instead of Gaussian ones or shorter wavelengths than the traditional lambda = 1.06 mu m. Surface mechanical effects are also theoretically and experimentally presented. They consist mainly of compressive residual stresses generated in the first 1-2 mm of depth that are the key to enhanced mechanical properties. The application of LSP to two new areas is presented. These areas are the improvement of the fatigue behavior in aluminum alloys and a thermomechanical treatment using both a CO2 laser for surface quenching and a pulsed Nd-glass laser for mechanical shock strengthening. Finally the attractive and detrimental features of LSP are discussed with the objective of defining an industrially convenient laser shock configuration.