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

Abstract

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 as-received 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.