YSZ/NiCrAlY interface oxidation of APS thermal barrier coatings

The interface oxidation induced microstructural evolution of air plasma spayed (APS) thermal barrier coatings (TBCs) is investigated. As the oxidation progresses, the thermally grown oxide (TGO) formed at the YSZ/NiCrAlY interface develops from a bi-layered structure, to a three-layered structure, then to a four-layered structure of Al2O3, Y3Al5O12 (YAG), NiCr2O4 and NiO, respectively. An oxidation mechanism is proposed to account for the growth of the layered TGO. The YAG formation consumes the underlying alumina layer and facilitates the outward diffusion of Cr and Ni, leading to a detrimental effect on the TBC life.