Mechanisms governing the thermal shock and tensile fracture of PS-PVD 7YSZ TBC

Thermal barrier coating (TBC) system including NiCoCrAlYTa metallic bond coating and 7YSZ (7 wt%Y2O3-ZrO2) ceramic top coating was deposited on nickel-based superalloy by plasma spray-physical vapor deposition (PS-PVD). Thermal shock property of 7YSZ TBC was characterized by water-quenching test at 1100 ℃ and its failure behaviors were investigated in detail. Besides, tensile test was performed for TBC sample and its cross-sectional fracture microstructure was studied as well. The results showed that after water-quenching test lots of pitting spallation took place in TBC surface, but no obvious microcracks were observed. Additionally, the tensile test indicated that fracture occurred in 7YSZ coating near the interface of ceramic-bond coating. After conduction of water-quenching and tensile testing, a lot of spherical particles and nano-sized agglomerated clusters were observed in the quasi-columnar structured 7YSZ coating. These lead to the formation of weak inter-column bonding and the failure of PS-PVD 7YSZ TBC. Moreover, in order to better understand the failure process, a deposition mechanism of coating was proposed.