Solidification behavior and Laves phase dissolution during homogenization heat treatment of Inconel 718 superalloy

The solidification behavior and microstructural evolutions during homogenization heat treatment of Inconel 718 superalloy were studied. The microstructure of the as-cast alloy was characterized by optical micrographs, scanning electron microscopy (SEM) images, and elemental analysis based on energy dispersive spectroscopy (EDS). The optimum etching techniques, especially electroetching, were characterized to reveal the dendritic nickel matrix, the microsegregation between dendrite arms, and the austenite/Laves eutectic structure. The elemental analysis of different microstructural features, especially the variation of the chemical composition of austenite, was successfully related to the pseudo-binary solidification constitution diagram. Moreover, the extension of the nonequilibrium eutectic isotherm was evaluated to unravel the solidification path of this important engineering alloy. The dissolution of the Laves phase and its kinetics during exposure at elevated temperatures with the purpose of homogenization were also discussed.