Effect of interaction of refractories with Ni-based superalloy on inclusions during vacuum induction melting

Abstract

This study documents laboratory-scale observation of the interactions between the Ni-based superalloy FGH4096 and refractories. Three different crucibles were tested—MgO, Al2O3, and MgO-spinel. We studied the variations in the compositions of the inclusions and the alloy-crucible interface with the reaction time using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and X-ray diffraction. The results showed that the MgO and MgO-spinel crucibles form MgO-containing inclusions (Al-Mg oxides and Al-Mg-Ti oxides), whereas the inclusions formed when using the Al2O3 crucible are Al2O3 and Al-Ti oxides. We observed a new MgAl2O4 phase at the inner wall of the MgO crucible, with the alloy melted in the MgO crucible exhibiting fewer inclusions. No new phase occurred at the inner wall of the Al2O3 crucible. We discuss the mechanism of interaction between the refractories and the Ni-based superalloy. Physical erosion was found to predominate in the Al2O3 crucible, whereas dissolution and chemical reactions dominated in the MgO crucible. No reaction was observed between three crucibles and the Ti of the melt although the Ti content (3.8wt%) was higher than that of Al (2.1wt%).