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 TiO 2 to improve their properties and corrosion resistance. It was found that TiO 2 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 TiO 2 promoted the densification of MgO crucibles by generating a liquid phase composed of TiO 2 -MgO-CaO-SiO 2 , resulting in a significant reduction in open porosity from 12.62% to 9.76% at a doping level of 5 wt.%. Moreover, TiO 2 alters the initial bonding phase from Ca 2 SiO 4 into CaTiO 3 , Mg 2 SiO 4 , and Mg 2 TiO 4 , enhancing thermal shock resistance by generating microcracks, lowering thermal expansion coefficient, and detaching the matrix/aggregate bonding. Notably, adding TiO 2 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, TiO 2 -doped MgO crucibles demonstrated superior performance compared to pure MgO and MgAl 2 O 4 crucibles.