Computer simulations of the evolution of solidification microstructure in the LENS™ rapid fabrication process

A modified cellular automaton-based method is developed to study the evolution of the solidification grain microstructure during the LENS™ rapid fabrication process. The method is coupled with a finite difference-based procedure for computation of the temperature field during both the substrate re-melting/feed-powder injection stage and the solidification stage of the LENS™ process. A distribution of the potency of nucleation sites is used to model heterogeneous nucleation both within the melt pool and at the substrate/melt interface. The dendrites are enabled to grow preferentially in the cubic crystallographic directions and the kinetics of dendrite-tips motion is assumed to be controlled by the local undercooling. The method developed enables the establishment of the relationships between the LENS™ process parameters (e.g. laser power, laser velocity), and the resulting solidification microstructure in any binary metallic material. The application of the model to Al–7.0 wt.% Si alloys yielded results which are in a generally good agreement with their experimental counterparts.