Thermal Conductivity, Phase Stability, and Oxidation Resistance of Y3Al5O12 (YAG)/Y2O3–ZrO2 (YSZ) Thermal-Barrier Coatings

This paper describes a new multilayer TBC that incorporates a 10 μm-thick oxygen barrier layer of yttrium–aluminum garnet (YAG) into a typical YSZ TBC system. The thermal conductivity of as-sprayed YAG/YSZ coatings was reduced due to excessive porosity and amorphous areas in the YAG layer. After long-term heat treatments, the conductivity of the multilayer was unaffected by the presence of YAG. Sintering and recrystallization of the amorphous YAG regions occurred during high-temperature heat treatments. While YAG itself possesses excellent phase stability, its presence also improved the phase stability of zirconia near the YAG/YSZ interface, inhibiting the outward diffusion of yttrium from high-yttria t-ZrO2 The YAG layer reduced the NiCoCrAlY bond-coat oxidation rate by a factor of three during isothermalfurnace tests conducted at 1200◦C.