Orientation dependence of microstructure and mechanical property in selective laser-melted Inconel 718 alloy

Inconel 718 alloy was fabricated by selective laser melting (SLM) technology under various parameters. Effect of orientation on microstructure characteristics and crystallographic texture of the SLM-ed alloy was systematically studied, and its integrated mechanical response was evaluated by combination of experiments and theoretical calculations. The microstructures of the SLM-ed alloy on the planes parallel to the build direction (XZ plane) and vertical to the build direction (XY plane) appeared scale-like molten pools with columnar dendrite and elongated molten channels with cellular structures, respectively. The contents of eutectic Laves phases on the XY plane were apparently higher than that on the XZ plane. A wire texture of 〈001〉//Z was exhibited on both planes of the SLM-ed alloy, but stronger intensity was displayed on the XZ plane. The SLM-ed alloy stretched along the XY direction owned higher tensile strength and yield strength but lower elongation. The calculated yield strengths were in good agreement with the experimental ones. Grain boundary strengthening was demonstrated to be the main factor for the discrepancies in yield strength of the alloy stretched along different directions. Smaller average Taylor factor (TF) caused by higher intensity of texture, as well as lower dislocation density (ρ) related to the kernel average misorientation (KAM) also contributed to the anisotropy in yield strength of the alloy, by influencing the dislocation strengthening.