Inconel 718 fabricated via arc-based directed energy deposition assisted with in situ interlayer hot forging

Ni-based superalloys fabricated by arc-based directed energy deposition (DED) typically exhibit a non-optimizedmicrostructure, characterized by coarse and oriented columnar grains, which limits their performance and in-dustrial applications. In this context, microstructure refinement techniques previously applied to arc-basedwelding have been tested in additive manufacturing, highlighting interlayer mechanical deformation methods(e.g., rolling and peening). The present work describes the grain size refinement mechanism of in situ interlayerhot forging (HF) and evaluates its effect on the elevated-temperature tensile behavior of Inconel 718 fabricatedvia DED (IN718 DED). HF induced a dynamically recrystallized zone (~1 mm) on the top layer surface and adeformed zone (~0.5 mm) immediately beneath it, which was not completely remelted by the subsequent layerdeposition, thereby generating recrystallized grains during subsequent multiple thermal cycles. During the ho-mogenization heat treatment, the remaining deformed region recrystallized, generating a finer grain size and analmost equiaxed microstructure. HF also improves the yield strength at elevated-temperatures and induces analmost isotropic behavior. For the first time, enabling the IN718 DED to meet the grain size, elongation, andelevated-temperature yield strength requirements (AMS 5662).