Effect of a MgO–CaO–ZrO2-based refractory on the cleanliness of a K4169 Ni-based superalloy

Abstract

Laboratory experiments were carried out to study the effect of a MgO–CaO–ZrO 2 -based refractory (MCZ refractory) on the cleanliness of a K4169 Ni-based superalloy. The chemical composition and characteristics of the refractory, alloy, and inclusions were analysed by X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS). Characterisation results indicated that the CaZrO 3 phase was stable, the amount of the spinel phase increased whereas that of the MgO phase decreased, and Ca 2 Al 2 SiO 7 and Ca 2 SiO 4 transformed into Ca 3 Ti 8 Al 12 O 37 and CaSiO 3 , respectively, in the refractory during the melting of the Ni-based superalloy. In addition, a new phase of Mg 8 Cr 16 O 32 was simultaneously formed. The MCZ refractory penetrated the liquid alloy and reacted with it, which increased the Mg and Ca contents of the alloy. The erosion depth of the refractory in the alloy was more than 20 μm after melting for 100 min. Inclusions composed of MgO–Al 2 O 3 -Ti x O y wrapped with TiN were observed in the alloy after melting in the MCZ refractory. The inclusions were large, numerous, and distributed inhomogeneously in the alloy near the side and bottom of the refractory. The chemical reactions among the refractory, liquid alloy, and inclusions were analysed, and FactSage software was used to investigate these interactions. The effect of the dissolution of the MCZ refractory on the composition and transformation of the liquid alloy and inclusion was estimated. The thermodynamic results agreed well with the experimental results.