The thermal behavior of CMAS-infiltrated thermal barrier coatings

Understanding the mechanisms by which the durability and functionality of thermal barrier coatings (TBCs) are compromised by the infiltration of molten calcium-magnesium alumino-silicates (CMAS) requires an assessment of the effects on the thermal and mechanical properties of the coating. This study focuses on quantifying the effect of CMAS on the thermal properties and heat transport in TBCs. The thermal properties of a 7 wt.% yttria-stabilized zirconia (7YSZ) TBC deposited on a superalloy substrate by air plasma spray (APS) were measured before and after CMAS infiltration. A rise in both volumetric heat capacity and thermal conductivity of the coating was observed upon infiltration. Calculations to explain these trends were performed for a model TBC system and found to be in good agreement with the measured results. The evolution of the phase constitution of the coating was analyzed by Raman spectroscopy and the integrity of the interface was characterized by optical examination of cross sections. These tests determined that the coating remained in good contact with the substrate and experienced no phase change after infiltration.