  Previous work on additively-manufactured oxide dispersion strengthened alloys
focused on experimental approaches, resulting in larger dispersoid sizes and
lower number densities than can be achieved with conventional powder
metallurgy. To improve the as-fabricated microstructure, this work integrates
experiments with a thermodynamic and kinetic modeling framework to probe the
limits of the dispersoid sizes and number densities that can be achieved with
powder bed fusion-laser beam. Bulk samples of a Ni-20Cr $+$ 1 wt.% Y$_2$O$_3$
alloy are fabricated using a range of laser power and scanning velocity
combinations. Scanning transmission electron microscopy characterization is
performed to quantify the dispersoid size distributions across the processing
space. The smallest mean dispersoid diameter (29 nm) is observed at 300 W and
1200 mm/s, with a number density of 1.0$\times$10$^{20}$ m$^{-3}$. The largest
mean diameter (72 nm) is observed at 200 W and 200 mm/s, with a number density
of 1.5$\times$10$^{19}$ m$^{-3}$. Scanning electron microscopy suggests that a
considerable fraction of the oxide added to the feedstock is lost during
processing, due to oxide agglomeration and the ejection of oxide-rich spatter
from the melt pool. After accounting for these losses, the model predictions
for the dispersoid diameter and number density align with the experimental
trends. The results suggest that the mechanism that limits the final number
density is collision coarsening of dispersoids in the melt pool. The modeling
framework is leveraged to propose processing strategies to limit dispersoid
size and increase number density.
