Effect of Molten-Salt Chemistry on Phase Evolution and Corrosion Degradation of Sc2O3-Y2O3 Co-Stabilized ZrO2 Thermal Barrier Ceramics

The corrosion resistance of electron-beam physical vapor-deposited (EB-PVD) zirconia thermal-barrier coatings depends on ceramic phase stability. Here, conventional 8YSZ and two Sc2O3-Y2O3 co-stabilized ZrO2 coatings, ScYSZ and ScYSZ with an Al-rich interlayer (ScYSZA), were comparatively investigated under three chloride-containing environments: NaCl (N) corrosion, high-temperature Na2SO4-NaCl (NN) corrosion, and Na2SO4-NaCl-V2O5 (NNV) corrosion. Phase evolution and microstructural degradation were examined by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy. Under N exposure, the ceramic top coats largely retained the tetragonal t′-ZrO2 phase, whereas degradation was concentrated near the ceramic/bond-coat interface. NN corrosion caused limited bulk phase transformation. The most pronounced degradation occurred under NNV exposure, particularly in 8YSZ, where extensive YVO4 formation and progressive t′→m transformation were accompanied by substantial disruption of the columnar ceramic structure. After 100 h of NNV corrosion, 8YSZ contained only 23.7 wt.% t′-ZrO2. In contrast, ScYSZ and ScYSZA retained 82.6 and 84.4 wt.% t′-ZrO2, respectively, confirming the superior phase stability and corrosion resistance of the ScYSZ-based coatings, particularly ScYSZA. These results demonstrate that chloride-containing environments produce distinct degradation pathways involving interfacial oxidation, corrosive-species ingress, and phase destabilization, highlighting the importance of integrating ceramic composition with coating architecture to improve the durability of EB-PVD thermal-barrier coatings.