Thermal Modelling of Pulsed Laser Ablation of Silicon Nitride Ceramics

Abstract

Pulsed laser systems have become a growing field in the past few years, especially in the treatment of the hard to machine engineering materials through conventional contact methods. As the challenge of the selection of efficient machining parameters is apparent, the modeled time dependent surface temperature and stress field evolution profiles will aid in improving the experimental design process. Due to the temperature gradient between the irradiated surface and the interior regions, excessive thermal residual stresses are induced in and around the heat affected zone. Depending on the laser intensity, the thermal stresses induced may lead to formation of micro-cracks and their propagation which can reduce the component fatigue life during its application. The current study aimed at understanding the evolution and distribution of thermal stresses on the material and to also evaluate the effect of laser energy intensity on the temperature and the induced thermal stresses. As a result of high temperatures involved, and a short interaction time associated with practical experiments, a computational approach in COMSOL Multiphysics was used. In the present research, the thermal modeling of High Frequency Nd:YAG in the machining of sintered silicon nitride ceramics was conducted. From the results, the model indicated that heating the target materials surface raises the temperature gradient which induced compressive thermal stresses. Two cycles were observed, the heating cycle where the laser was ON (0–250 ns) and cooling cycle during laser OFF time (after 250 ns).