Enhancing high-temperature oxidation resistance in directed energy deposition-processed Ni-based superalloys via heat treatment

Ni-based superalloys produced via additive manufacturing (AM) face challenges in achieving optimal oxidation resistance due to elemental segregation and microstructural anisotropy inherent to the process. In this work, the oxidation resistance of additively manufactured Ni-based superalloys AMS-OR was remarkedly improved by heat treatment, reducing mass gain by 35 %, and oxide layer thickness by 38 % compared to the as-printed condition. This enhancement arises from microstructural optimization during heat treatment: Dendritic W segregation is eliminated through heat treatment, which redistributes aluminum into the γ matrix. This redistribution, combined with a lower oxygen partial pressure resulting from the coarser spinel grains in the oxide layer, enhances Al availability and promotes the formation of a continuous, protective Al₂O₃ layer. In addition, the localized W enrichment in dendritic cores in the as-printed alloy led to the formation of volatile WO₃, causing porous oxide morphologies and transient mass loss. Heat treatment suppresses WO₃ evolution by homogenizing W distribution, while partial dissolution of interdendritic (Nb,Ta)C carbides further stabilizes the oxide structure. By prioritizing microstructural homogenization over compositional changes, this work demonstrates that post-build heat treatment effectively addresses oxidation challenges in additive manufacturing, offering a scalable strategy to enhance high-temperature durability for aerospace and energy applications.