  A broad range of computational models have been proposed to predict
microstructure development during solidification processing but they have
seldom been compared to each other on a quantitative and systematic basis. In
this paper, we compare phase-field (PF) and cellular automaton (CA) simulations
of polycrystalline growth in a two-dimensional melt pool under conditions
relevant to additive manufacturing (powder-bed fusion). We compare the
resulting grain structures using local (point-by-point) measurements, as well
as averaged grain orientation distributions over several simulations. We
explore the effect of the CA spatial discretization level and that of the melt
pool aspect ratio upon the selected grain texture. Our simulations show that
detailed microscopic features related to transient growth conditions and
solid-liquid interface stability (e.g. the initial planar growth stage prior to
its cellular/dendritic destabilization, or the early elimination of unfavorably
oriented grains due to neighbor grain sidebranching) can only be captured by PF
simulations. The resulting disagreement between PF and CA predictions can only
be addressed partially by a refinement of the CA grid. However, overall grain
distributions averaged over the entire melt pools of several simulations seem
to lead to a notably better agreement between PF and CA, with some variability
with the melt pool shape and CA grid. While further research remains required,
in particular to identify the appropriate selection of CA spatial
discretization and its link to characteristic microstructural length scales,
this research provides a useful step forward in this direction by comparing
both methods quantitatively at process-relevant length and time scales.
