Investigating the corrosion resistance of calcium zirconate in contact with titanium alloy melts

This study investigated the corrosion behavior of calcium zirconate crucibles during vacuum induction melting of Ti–6Al–4V. Due to its production method the fused calcium zirconate raw material contained a significant amount of cubic zirconia as a second phase. Thus, the raw material composition was adjusted by adding calcium hydroxide as a calcia precursor during the crucible production. Crucibles with four different compositions were tested in contact with Ti–6Al–4V melts. The corroded crucibles were investigated by SEM in combination with EDX and EBSD, whereas a dissolution of the zirconia phase by the alloy melt was observed. The calcium zirconate phase however remained unaffected. This result compared well with the determined zirconium and oxygen contamination of the melts, which decreased substantially with a higher calcium zirconate content of the crucibles. An overstoichiometric composition in terms of calcia, however, caused the evaporation of calcia and should therefore be avoided.