Impact of fluid flow on the dendrite growth and the formation of new grains in additive manufacturing

Manipulating the formation of new grains in metal additive manufacturing (AM) is critical for tailoring the grain structure in the as-built components. Temperature gradient and solidification velocity are believed the main factors controlling the formation of new grains, while the impact of fluid flow in AM has never been investigated. In this work, the multi-grid dendrite growth model is improved by two-way coupling with a computational fluid dynamics model to simulate the dendrite growth in the flowing liquid metal under various temperature gradients and solidification velocities found in AM condition, thereby studying the impact of fluid flow on the dendrite growth and the formation of new grains in front of dendrites with various orientations. The simulation results reveal that dendrite growth and the formation of new grains in AM are influenced by the fluid flow and solidification significantly and in similar manner as that in casting. Furthermore, molten-pool scale dendrite growth simulations are carried out with the temperature field and flow field data extracted from the thermal-fluid flow modeling results. The simulation results well explain the formation mechanism of the grain structure in the single-track experiments with electron beam and laser, and further demonstrate the remarkable impact of fluid flow on dendrite growth and the formation of new grains in AM.