MICROSTRUCTURE AND PHASE-COMPOSITION OF ZRO2-CEO2 THERMAL BARRIER COATINGS

The microstructure and phase composition of zirconia plasma-sprayed thermal barrier coatings containing 12 to 25 wt % ceria addition have been investigated. Coatings containing less than 20 wt % CeO2 are composed of a monoclinic and retained metastable transformable tetragonal phase due to the constraint developed by the small crystal size. This phase transforms readily under moderate thermal stresses. Compositions greater than 20 wt % CeO2 are composed only of a metastable non-transformable tetragonal, tz' structure, resistant to transformation under thermal or mechanical stresses. The microstructure of this phase shows microstructural similarities to the high-yttria t'-phase in the ZrO2-Y2O3 system, such as transformation twins and anti-phase boundaries. This suggests that the phase observed in the ZrO2-CeO2 system forms by a similar mechanism.