Microstructure and phase composition of ZrO2-CeO2 thermal barrier coatings

Abstract

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.