J. W. Newkirk, University of Missouri-Rolla, Rolla, MO; Z. Fan, F. Liou, Missouri University of Science & Technology, Rolla, MO
A multiscale model for the laser deposition process has been developed. The multi-scale model consists of two parts at different levels: a macroscopic model to model mass, heat and momentum transfer, and a microscopic model to model the evolution of solidification and solid phase transformation microstructures during laser deposition. These two models are fully coupled. At the macroscopic scale, a comprehensive mathematical model and the associated numerical technique have been developed to simulate the coupled, interactive transport phenomena between the laser, the powder, and the substrate during the laser deposition process. The simulation involves laser material interaction, free surface evolution, droplet formation, transfer and impingement onto the substrate, and melt-pool dynamics. Transient temperature and velocity distributions of the falling particles, shape of the falling particles and melt pool, and heat transfer and fluid flow in the melt pool are all calculated in a single, unified model, using the continuum formulation and the volume of fluid technique. At the microscopic scale, a stochastic microstructure model is developed to simulate dendritic grain structures and morphological evolution in solidification. The model is based on the cellular automata approach, which takes into account the heterogeneous nucleation both within the melt pool and at the substrate/melt interface, the growth kinetics, and preferential growth directions of dendrites. Both diffusion and convection effects are included, for which the input parameters are from the macroscopic model. This model enables prediction and visualization of grain structures during and after the deposition process. In the model, solid phase transformation is also modeled with application to Ti-6Al-4V. The coupling between macroscopic and microscopic simulations is performed using different time steps and mesh sizes, with those for microscopic simulation much finer. Adaptive time steps are adopted for both macroscopic and microscopic simulations.
Summary: A multiscale model for the laser deposition process has been developed and will be presented in this session. The multi-scale model consists of two parts at different levels: a macroscopic model to model mass, heat and momentum transfer, and a microscopic model to model the evolution of solidification and solid phase transformation microstructures during laser deposition.
