Na2O is volatile at high temperatures, and is the most likely the cause of the large voids in Region 1 of the 7YSZ TBC (Fig. 1B) after attack by Na-rich CMAS for 24 h (1340 ◦C). This is supported by the observed decrease in Na+in the system with an increase in the exposure duration (Table 1), and in a separate experiment a significant loss of Na2O is also measured after the glass frit was heat treated for 24 h at 1340 ◦C. The resulting voids destroy the coating’s structure and cause the free-standing coating to bend. Bending implies delamination from the substrate in a TBC system, which has been observed by Shan et al.
Fig. 1.BSE-SEM micrographs of 7YSZ TBCs after attack by (A,C, and E) sand-CMAS and | 