Ni-based superalloy 718 fabricated by arc-based directed energy deposition: an experimentally-based strengthening mechanisms analysis

The present work describes and quantitatively assesses the strengthening mechanisms in Inconel 718 fabricated by arc-based DED (IN718 arc-based DED) through an experimentally-based approach. IN718 arc-based DED (in the as-built condition) showed a typical coarse (millimetric-sized grains) and oriented (cube texture) microstructure with a significant quantity of interdendritic eutectics (Laves and MC-type carbides). After heat treatment (1100 °C/2 h + aging), these eutectics were partially dissolved; however, the original grain size and crystallographic texture aspects were not altered. In addition, the heat treatment promoted a notorious γ′′ (Ni3Nb) and γ′ (Ni3(Al, Ti)) phases content (∼17 and 5 %, respectively), which results in superior room temperature tensile strength despite the aforementioned non-optimized microstructure. The grain size, dislocation density, precipitation content and morphology, and alloying elements in solid solution were experimentally measured and utilized as input data for a quantitative assessment of the strengthening mechanisms. This analysis concludes that the linear dependence of the majority of the strengthening mechanisms on the Taylor factor predominantly promoted the yield strength anisotropy. Furthermore, as expected, it is evidenced that the precipitation strengthening mechanism governs the final strength of IN718 arc-based DED.