Oxidation Performance of Inconel 718 Alloy Fabricated by Directed Energy Deposition

Directed energy deposition (DED) is an additive manufacturing process that uses a focused energy source, such as a laser, to melt and deposit material layer-by-layer to create 3D complex parts. This study investigated the effects of laser power on the microstructure, hardness, and oxidation performance of IN718 superalloy fabricated via DED process. The DED-processed samples underwent heat treatment (solution treatment and ageing) and were compared with the as-built counterpart, as a baseline for this experimental analysis. Microstructural characterization utilized an optical microscope and a field emission scanning electron microscope (FESEM). Vickers microhardness measurements were performed. In situ thermogravimetric analysis (TGA) was conducted at 850 °C for 5 h, followed by SEM characterization. The findings revealed microstructural variations in the as-built samples with increasing laser power. As-built samples have a dendritic microstructure with fine equiaxed grains. The solutionizing heat treatment dissolves and redistributes the γ″ and γ′ precipitates, resulting in a more uniform and stable microstructure. Aged samples have a uniform distribution of large and uniform coherent γ″ and γ′ precipitates. Hardness values remain relatively unchanged in as-built samples, but aged samples exhibit increased hardness due to the formation of precipitates during heat treatment. The study also found that, in the as-built condition, the sample produced with the lowest laser power had the highest oxidation resistance, while the solutionized and aged samples produced with higher laser power had better oxidation resistance due to the formation of protective oxide layers and precipitates. This study provides insights for optimizing process parameters and heat treatments to enhance the performance of DED-fabricated IN718 alloy components for high-temperature applications.