Development of TiO2-doped MgO refractories with enhanced corrosion resistance for preparing high-purity nickel-based superalloys

MgO refractories extensively applied in melting nickel-based superalloys are limited by their poor thermal shock resistance and susceptibility to melt erosion. This study regulated the phase composition of MgO refractories by doping TiO2 to improve their properties and corrosion resistance. It was found that TiO2 is an effective dopant, addressing key limitations such as hard sintering, inadequate thermal shock resistance, and insufficient chemical stability. Firstly, the strong sintering ability of TiO2 promoted the densification of MgO crucibles by generating a liquid phase composed of TiO2–MgO–CaO–SiO2, resulting in a significant reduction in open porosity from 12.62% to 9.76% at a doping level of 5 wt%. Moreover, TiO2 alters the initial bonding phase from Ca2SiO4 into CaTiO3, Mg2SiO4, and Mg2TiO4, enhancing thermal shock resistance by generating microcracks, lowering thermal expansion coefficient, and detaching the matrix/aggregate bonding. Notably, adding TiO2 enhanced the corrosion resistance of MgO ceramic crucibles, reducing the total impurity content in the alloy from 0.0021 wt% to 0.0007 wt%. In summary, TiO2-doped MgO crucibles demonstrated superior performance compared to pure MgO and MgAl2O4 crucibles.