Synergistic effect of MgO and CeO₂ in the slag on non-metallic inclusions of high Al nickel-based superalloy during electroslag remelting

The effect of MgO and CeO 2 in the slag on the modification and removal of non-metallic inclusions in a high Al nickel-based superalloy during electroslag remelting was investigated. Chemical reactions between MgO and CeO 2 in the slag and dissolved Al in the alloy led to dissolved Ce and Mg. Dissolved Mg changed original polygonal MgO-Al 2 O 3 inclusions to spherical MgO-Al 2 O 3 with increasing MgO content, while dissolved Ce replaced Mg and Al of the inclusions and changed inclusions to Ce 2 O 3 -Al 2 O 3 -MgO. The content of O and the number of inclusions decreased significantly in case of rare earth bearing slag with high CeO 2 /Al 2 O 3 mass ratio. The whole interfacial reactions were: MgO(slag) + CeO 2 (slag) + 2[Al] Ni (l) = Al 2 O 3 (slag) + [Mg] Ni (l) + [Ce] Ni (l), and Al 2 O 3 (inclusion) + [Mg] Ni (l) + [Ce] Ni (l) = MgO(inclusion) + CeO 2 (inclusion) + [Al] Ni (l).