Microscopic observation of degradation behavior in yttria and ceria stabilized zirconia thermal barrier coatings under hot corrosion

Abstract

In this study, the effects of yttria stabilizer replacement with ceria on hot corrosion properties of thermal barrier coatings (TBCs) have been investigated in microscopic respects. Yttria stabilized zirconia (YSZ; ZrO 2–8 wt.%Y 2O 3) and ceria stabilized zirconia (CSZ; ZrO 2–25 wt.%CeO 2–2.5 wt.%Y 2O 3) thermal barrier coatings (TBCs) were fabricated to have similar microstructures, followed by hot corrosion tests with a NaVO 3 salt at 900 °C. Very dense YSZ TBCs with porosities below 4% were also fabricated in order to investigate the effects of coating defects on hot corrosion behavior. Results revealed that CSZ TBCs were better resistant to hot corrosion environment than YSZ TBCs in terms of phase stability and overall damage by the salt. From studies on microscopic failure behavior, it was found that YSZ and CSZ TBCs showed a different degradation behavior and that coating defects, such as pores, microcracks and splat boundaries, play important roles as effective paths for the salt in hot corrosion. From the present results, a possible microscopic degradation mechanism and effects of coating microstructures for zirconia-based TBCs under hot corrosion are discussed.