Physics and applications of laser shock processing of materials

Abstract

Shock waves induced by laser-plasma in Water Confinement Regime (WCR) are used in order to improve the metallurgical properties of metallic materials. In a first part of this paper we discuss the basic principles which limit the pressure generation in this regime: the effects of laser intensity, target material, laser pulse duration and laser wavelength are discussed. Depending on laser parameters, the peak pressure is saturated and its duration is reduced above a laser intensity threshold, due to laser-induced breakdown plasma in the confining water. The observation of the interaction zone shows that this parasitic breakdown occurs only at the water surface and limits the efficiency of the process. The relative influence of main physical mechanisms occurring during the generation of the laser breakdown at the surface of water have been discussed. According to the wavelength effect which tends to authorize higher pressure with longer wavelengths, the influence of multiphotoionic processes dominates the effect of avalanche ionization. The second part of the paper deals with the surface modifications induced by laser-shock processing. Depending on the operating parameters, Residual Stresses (RS) field can be optimized. Typical present or future applications such as the improvement of fatigue or corrosion properties, are then presented.