Additive manufacturing by selective laser melting (SLM) is accompanied by solidification under large thermal gradients and cooling rates. As a consequence, solidification morphologies between dendritic with only limited sidebranches or rather cellular pattern are commonly observed. The growth regime is characterised by Péclet numbers larger 1, i. e. with cell tip radii larger than the diffusive pile-up in the melt, thus the applicability of models for dendritic growth developed for lower solidification velocities is quite limited.
We will present results from 2D and 3D phase-field simulations of primary solidification of the Ni based alloy IN718 for a range of solidification rates (0.5 … 5 cm/s) and temperature gradients (10^5 K/cm … 10^6 K/cm) typically seen in SLM. The operating state of the growth front will be discussed in terms of cell tip shapes, growth undercooling, primary spacing and the effect of crystallographic orientation. A general observation is that for higher Péclet numbers spacing selection is less effective. Cellular morphologies and spacing variations show a remarkable agreement with experimental data for IN718.