  Numerical simulations are used in this work to investigate aspects of
microstructure and microsegregation during rapid solidification of a Ni-based
superalloy in a laser powder bed fusion additive manufacturing process. Thermal
modeling by finite element analysis simulates the laser melt pool, with surface
temperatures in agreement with in situ thermographic measurements on Inconel
625. Geometric and thermal features of the simulated melt pools are extracted
and used in subsequent mesoscale simulations. Solidification in the melt pool
is simulated on two length scales. For the multicomponent alloy Inconel 625,
microsegregation between dendrite arms is calculated using the Scheil-Gulliver
solidification model and DICTRA software. Phase-field simulations, using Ni-Nb
as a binary analogue to Inconel 625, produced microstructures with primary
cellular/dendritic arm spacings in agreement with measured spacings in
experimentally observed microstructures and a lesser extent of microsegregation
than predicted by DICTRA simulations. The composition profiles are used to
compare thermodynamic driving forces for nucleation against experimentally
observed precipitates identified by electron and X-ray diffraction analyses.
Our analysis lists the precipitates that may form from FCC phase of enriched
interdendritic compositions and compares these against experimentally observed
phases from 1 h heat treatments at two temperatures: stress relief at 1143 K
(870{\deg}C) or homogenization at 1423 K (1150{\deg}C).
