Study on the stability of different refractories during the melting process of a K4169 Ni-based superalloy

Abstract

The composition of the refractory strongly affects the cleanliness of the alloy. K4169 Ni-based superalloys were melted in different types of refractories in this study. The cleanliness of the Ni-based superalloy and phase transformation of the refractory were observed by X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy energy dispersive spectroscopy (SEM‒EDS). The high-temperature stabilities of a Y2O3-based refractory, MgO-based refractory, and Al2O3-based refractory during melting with a Ni-based alloy were compared. The oxygen content was also lowest, and no Y2O3-containing inclusions were observed in the Ni-based alloy melted with the Y2O3-based refractory at 1823 K. Inclusions with 21%–29% MgO and a phase composed of Al, Mg and O with an area of approximately 1300 μm2 were observed in the alloy. This indicates that the dissolution and erosion of the Y2O3-based refractory were weak, and obvious physical erosion and chemical dissolution of the MgO-based refractory occurred during the melting process of the Ni-based alloy. The width of the refractory phase adhered to the boundary of the Ni-based alloy increased in the order Y2O3-based refractory (15 μm- 23 μm)< Al2O3-based refractory (93 μm- 285 μm)< MgO-based refractory (3.5 mm–3.6 mm), indicating that the adhesive strength of the MgO-based refractory with the Ni-based alloy was strongest. The interaction between the refractory material, Ni-based alloy and inclusions was analyzed based on thermodynamic calculations by Factsage software. The effects of dissolution of the three refractory types on the formation and transformation of the new phases and inclusions were estimated. The thermodynamic results were in good agreement with the experimental results.