Microstructure and fatigue crack growth behavior of Inconel 718 superalloy manufactured by laser directed energy deposition

Abstract In this study, Inconel 718 (IN718) specimens, manufactured by laser directed energy deposition (LDED), are subjected to three different heat-treatments to have different microstructural characteristics. Fatigue crack growth (FCG) testing is performed on both as-deposited and heat-treated specimens. The coarse Laves phases with uneven γ′′/γ′ precipitates severely decrease FCG resistance of LDED IN718. The soft precipitate-free zone around short-acicular δ-phase partly reduces FCG resistance of LDED IN718. The FCG threshold ( Δ K th ) of a judicious heat-treatment specimen increases by ∼2.6 times vs. as-deposited specimen and reaches 10.8 MPa∙m1/2, and its Δ K th and FCG curve are comparable to those of wrought IN718.