Microstructural Evolution and Strength of 3D Printed and Directly Aged ODS-Strengthened Inconel718

Abstract The high-temperature capability of Inconel718 is limited by the coarsening and dissolution of its primary strengthening phase, the γ ′′ precipitates. To enhance its performance, this study introduces oxide-dispersion strengthening (ODS) particles by coating alloy powder with nanoscale yttria via resonant acoustic mixing, followed by laser powder bed fusion. Multi-scale, multi-modal electron microscopy was used to examine the effects of direct aging on both ODS and non-ODS alloys. Apart from the oxides themselves, ODS particles do not alter the distribution or morphology of microstructural constituents, including γ ′ and γ ′′ precipitates, γ ′/ γ ′′ coprecipitates, Laves phases, carbides, and δ phases. Along dislocation cell walls, δ phases form with growth defects, predominantly after higher temperature aging treatments. In contrast, δ phases along high-angle grain boundaries are predominantly defect-free in all conditions but occasionally incorporate thin η phase layers. Yttrium oxides are preferentially located along dislocation cell walls, adopt either a trigonal (P-3m1) or cubic (Ia-3) crystal structure, and remain nearly stoichiometric Y 2 O 3 with only minor Al and occasional Ti enrichment. While the addition of ODS particles produce only modest increases in the yield strength at elevated temperatures, they significantly improve ductility, mitigating the characteristic intermediate-temperature embrittlement of additively manufactured Inconel718.