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.