  Predicting the microstructure during selective laser sintering (SLS) is of
great interests, which can compliment the current time and cost expensive
trial-and-error principle with an efficient computational design tool. However,
it still remains a great challenge to simulate the microstructure evolution
during SLS due to the complex underlying physical phenomena.
  In this work, we present a three-dimensional finite element phase-field
simulation of the SLS single scan, and revealed the process-microstructure
relation. We use a thermodynamically consistent non-isothermal phase-field
model including various physics (i.e. partial melting, pore structure
evolution, diffusion, grain boundary migration, and coupled heat transfer), and
interaction of powder bed and laser power absorption. The initial powder bed is
generated by the discrete element method. Moreover, we present in the
manuscript a novel algorithm analogy to minimum coloring problem and managed to
simulate a system of 200 grains with grain tracking using as low as 8
non-conserved order parameters. The developed model is shown to capture
interesting phenomena which are not accessible to the conventional isothermal
model. Specifically, applying the model to SLS of the stainless steel 316L
powder, we identify the influences of laser power and scanning speed on
microstructural indicators, including the porosity, surface morphology,
temperature profile, grain geometry, and densification. We further validate the
first-order kinetics during the porosity evolution, and demonstrate the
applicability of the developed model in predicting the linkage of densification
factor to the specific energy input during SLS.
