Unusually high room and elevated-temperature tensile properties observed in direct aged wire-arc directed energy deposited Inconel 718

Abstract

Wire-arc directed energy deposition (DED) processed Inconel (IN) 718 is known to have coarse columnar grains, strong texture, and significant chemical and microstructural inhomogeneity in the as-fabricated condition. Homogenization treatment is commonly used prior to aging to eliminate the inhomogeneity and detrimental precipitation for better mechanical properties. In this study, however, direct aging (DA) at 700 °C without homogenization has resulted in room-temperature yield strength, ultimate tensile strength (UTS), and elongation that are comparable to wrought condition and among the highest reported properties for wire-arc DED IN718. The DA samples at between 650 and 750 °C aging also demonstrates remarkable ductility when deformed at elevated temperatures. In addition, when aged below 750 °C the DA IN718 possesses significantly higher UTS compared to those with homogenization treatment. These superior mechanical properties are highly likely due to the non-uniform and hierarchical precipitation consisting of disk-shaped γ″ in diameter from a few to tens of nm in the dendritic core area and micron-sized Laves phase and carbides in the inter-dendritic region.