Simulations of microstructure coupling with moving molten pool by selective laser melting using a cellular automaton

Alloys produced by the selective-laser-melting process have excellent mechanical properties and their microstructures are significantly different from conventional cast alloys. In this paper, a model for predicting alloy microstructure coupling with heat transfer and a moving molten pool was developed using a cellular automata method, and the microstructure morphology and formation mechanism were numerically investigated. The growth kinetics of the solid/liquid interface is driven by the thermodynamic, composition and curvature undercooling, and the growth rate is computed by the Kurz-Giovanola-Trivedi model. The thermal history, cooling rate, molten pool, solidified track, grain growth, and undercooling were qualitatively analyzed by using the developed model. A complex dendritic growth mechanism including homogeneous and heterogeneous nucleations, competitive growth, and epitaxial growth was presented, and the effects of scanning speed, scanning spacing, and pre-heating temperature on the microstructure were examined. The results indicate that the cooling rate is approximately 10⁵–10⁶ K/s during the solidification, the equiaxed crystals increase with either increasing the pre-heating temperature or reducing the scanning speed. The epitaxial columnar grains become longer and narrower with increasing scanning spacing.