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Ni-based superalloys fabricated by arc-based directed energy deposition (DED) typically exhibit a non-optimized microstructure, characterized by coarse and oriented columnar grains, which limits their performance and industrial applications. In this context, microstructure refinement techniques previously applied to arc-based welding 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 interlayer hot forging (HF) and evaluates its effect on the elevated-temperature tensile behavior of Inconel 718 fabricated via DED (IN718 DED). HF induced a dynamically recrystallized zone (∼1 mm) on the top layer surface and a deformed zone (∼0.5 mm) immediately beneath it, which was not completely remelted by the subsequent layer deposition, thereby generating recrystallized grains during subsequent multiple thermal cycles. During the homogenization heat treatment, the remaining deformed region recrystallized, generating a finer grain size and an almost equiaxed microstructure. HF also improves the yield strength at elevated-temperatures and induces an almost isotropic behavior. For the first time, enabling the IN718 DED to meet the grain size, elongation, and elevated-temperature yield strength requirements (AMS 5662).
Farias et al. (Mon,) studied this question.