Evaluation of Ca-doped BaZrO3 as the crucible refractory for melting TiAl alloys

In this study, a new Ca-doped BaZrO3 refractory was designed by using thermodynamics approaches and tested for its applicability for vacuum induction melting (VIM) of TiAl alloys. The influence of CaO on the BaZrO3 phase constitution and microstructure, as well as the key features of the TiAl melt interaction with the Ca-doped BaZrO3 crucibles were investigated by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). Results revealed that the Ca-doped BaZrO3 refractory consisted of Ba1-xCaxZrO3 and CaO phases. An obvious interaction occurred during the melting of the TiAl alloy in the Ca-doped BaZrO3 crucible along with the generation of BaAl2O4 as a reaction product, with formation of a reaction layer up to 5 µm thick. Dissolution of Ca-doped BaZrO3 refractory in the TiAl melt was the main reason for the alloy-crucible reaction. Moreover, the Ca-doped BaZrO3 crucible was found to substantially reduce the contamination of the TiAl alloy, with lower oxygen concentration as compared with other conventional oxide crucibles. Overall results confirmed that vacuum induction melting using the Ca-doped BaZrO3 refractory can be considered as an appropriate method for the fabrication of TiAl alloys.