Microstructural Investigation of Inconel 718 Superalloy in the As-Cast and Homogenized Conditions

The microstructure of Inconel 718 superalloy in the as-cast (vacuum arc remelted and cast in a water-cooled copper mold) and homogenized conditions was studied. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for microstructural studies and elemental analysis, respectively. The presence of austenite/Laves eutectic constituent and carbides was discussed based on the phase diagram and the microsegregation of niobium and molybdenum between dendrite arms of the austenite matrix. In the eutectic structure, the amount of Nb was estimated to be ~ 20 wt%, which is much higher than the corresponding value of ~ 5 wt% in the original chemical composition of the alloy. Based on the elemental analysis, the Laves phase and carbides were characterized as Ni2Nb and MC, respectively. The dissolution of the Laves phase and the disappearance of the dendritic structure as a result of the elevated temperatures homogenization were also studied and it was revealed that the carbide particles remain in the microstructure after homogenization.