Anomalous 3D internal oxide network formation in Ni-based superalloy 247 processed by electron beam powder bed fusion additive manufacturing

Using FIB–SEM tomography, we reveal an anomalous three‑dimensional internal alumina network that forms during high‑temperature oxidation (1100 °C) of an electron‑beam powder bed fusion (PBF‑EB) Ni‑based superalloy 247. This network develops beneath the external scale and preferentially forms around an interconnected skeleton of refined carbides. While conventional 2D cross‑sections suggest isolated oxide–carbide co‑precipitates, three‑dimensional reconstructions show that all internal oxides are topologically connected, forming a continuous network. Time‑resolved exposures (5 min, 30 min, 50 h) demonstrate that directional carbide agglomeration during isothermal holding builds the skeleton for subsequent alumina growth, as carbide/matrix interfaces act as high‑diffusivity oxygen pathways and are enriched in Al. Based on these observations, we propose a mechanism of internal oxidation governed by carbide dissolution and directional agglomeration. The findings are compared with a conventionally cast alloy, oxidized for 50 h at 1100 o C, where the internal oxidation front was not associated with carbides and shows lower percolation depth and interconnectivity. The above benchmarking indicates that the agglomeration of finely distributed carbides during oxidation of PBF-EB led to the formation of the unique internal oxide-carbide network.