Numerical simulation of microstructure evolution during laser directed energy deposition for Inconel 718 using cellular automaton method coupled with Eulerian multiphase

A multi-scale cellular automaton-Eulerian multiphase model is employed to predict the dendritic and grain structure during the laser directed energy deposition of Inconel 718. Simulated transient temperature histories form the macro-scale Eulerian multiphase model are used as input data to the micro-scale microstructure simulation. A complex microstructure evolution mechanism including the epitaxial growth of dendrites from the substrate, heterogeneous nucleation, competitive growth between epitaxial columnar grains, nucleated columnar grains and equiaxed grains was presented, and the influence of the transient thermal history on the primary dendrite arm spacing is discussed. By comparing the simulated solidification microstructure of the melt pool with the experimental results, the accuracy of the coupled model was verified. The results show a reduction in the primary dendrite arm spacing from 12.8 & mu;m to 8.3 & mu;m from the bottom to the top of the melt pool. According to the aspect ratio of the grains in the melt pool, the top area has 40% equiaxed grains and 60% columnar grains, while the bottom area has 8% equiaxed grains and 92% columnar grains.