Effects of YSZ deposition process on reactive elements distribution and cyclic oxidation behaviors of a thermal barrier coating system

Abstract

Three coatings including topcoat-free NiCoCrAlYHfZr bond coat and the thermal barrier coating (TBC) system consisting of an 8 wt% Y2O3 stabilized ZrO2 (8YSZ) topcoat and either a NiCoCrAlYHfZr or a NiCoCrAlY bond coat were prepared in this study. The localized enrichment of Hf-rich precipitations within NiCoCrAlYHfZr bond coat was significantly alleviated after the YSZ deposition, instead, the nano-sized HfO2 precipitations formed and linearly distributed along the initial thermal grown oxide (TGO)/bond coat interface. Cyclic oxidation behaviors of the three coatings were evaluated at 1100 °C. The results showed that a uniform TGO with fine reactive elements (REs)-rich inclusions was generated in YSZ-NiCoCrAlYHfZr TBC system, alleviating the negative effects resulted from the localized enrichment of Hf-rich precipitations. Besides, co-doping HfZr in NiCoCrAlY bond coat prevented the formation of spinel since HfZr segregating at Al2O3 grain boundaries inhibited the outward diffusion of Ni, Co and Cr from the bond coat, thus significantly improving durability of the TBC system.