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Previous work on additively-manufactured oxide dispersion strengthened alloysfocused on experimental approaches, resulting in larger dispersoid sizes andlower number densities than can be achieved with conventional powdermetallurgy. To improve the as-fabricated microstructure, this work integratesexperiments with a thermodynamic and kinetic modeling framework to probe thelimits of the dispersoid sizes and number densities that can be achieved withpowder 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 velocitycombinations. Scanning transmission electron microscopy characterization isperformed to quantify the dispersoid size distributions across the processingspace. The smallest mean dispersoid diameter (29 nm) is observed at 300 W and1200 mm/s, with a number density of 1.0$\times$10$^{20}$ m$^{-3}$. The largestmean diameter (72 nm) is observed at 200 W and 200 mm/s, with a number densityof 1.5$\times$10$^{19}$ m$^{-3}$. Scanning electron microscopy suggests that aconsiderable fraction of the oxide added to the feedstock is lost duringprocessing, due to oxide agglomeration and the ejection of oxide-rich spatterfrom the melt pool. After accounting for these losses, the model predictionsfor the dispersoid diameter and number density align with the experimentaltrends. The results suggest that the mechanism that limits the final numberdensity is collision coarsening of dispersoids in the melt pool. The modelingframework is leveraged to propose processing strategies to limit dispersoidsize and increase number density.

Limits of dispersoid size and number density in oxide dispersion strengthened alloys fabricated with powder bed fusion-laser beam