Investigation of eutectic island formation in SX superalloys

We investigated whether the nucleation of the eutectic islands in superalloy solidification occurs in the interdendritic bulk liquid or at the dendrite-melt interface. Directionally solidified samples of CMSX-4 and a model superalloy have been analysed by means of light and electron microscopy and by EBSD measurements. For some samples, the solid-melt interface has been revealed by an artificial bubble technique. Additionally, thermodynamic calculations on phase formation and nucleation work as well as phase-field simulations have been performed, using ThermoCalc and MICRESS. The results indicate a kind of epitaxial nucleation mechanism at the solid-liquid interface of the primary γ dendrites.