Microstructural evolution and mechanical properties of Y2O3 reinforced IN718 superalloys fabricated by laser directed energy deposition

Laser directed energy deposition (LDED) presents a promising approach for fabricating and repairing intricate components made from oxide dispersion-strengthened nickel-based superalloys. However, the evolution of oxides during the LDED process and their contributions to the mechanical properties remain insufficiently explored. This study investigated the effects of Y2O3 additions on the microstructure and mechanical properties of asreceived and heat-treated states IN718 alloys and the evolution mechanism of Y2O3 in the melt pool. During the LDED process, a certain fraction of Y2O3 melts and decomposes in the melt pool, reacting in situ with Al to form Al2O3-Y4Al2O9 composite oxides. The Y2O3 and composite oxide nanoparticles act as heterogeneous nucleation sites, refining the dendritic and grain structures. With increasing the Y2O3 addition, the strength of the alloys increases. Notably, the IN718 alloys with 1.0 wt% Y2O3 achieve the optimal strength-toughness balance, elevating the room temperature yield strength by 35.7% compared to the as-received sample without Y2O3 addition. After heat treatment, the IN718 alloys with 1.0 wt% Y2O3 elevate the room temperature yield strength by 4.9% and the high temperature yield strength by 13.4% while exhibiting a more pronounced dynamic strain aging effect than the sample without Y2O3 addition. Besides, the oxides showcase a certain deformability owing to the presence of dislocations in the interior, thereby preventing the crack nucleation near the oxides upon tensile straining. This study provides novel insights into enhancing the mechanical properties of additively manufactured IN718 alloys.