Oxidation behavior of the monolayered La2Zr2O7, composite La2Zr2O7 + 8YSZ, and double-ceramic layered La2Zr2O7/La2Zr2O7 + 8YSZ/8YSZ thermal barrier coatings

Abstract

The degradation process of thermal barrier coatings (TBCs) such as monolayered La2Zr2O7, composite 50% La2Zr2O7 + 50% 8YSZ, and double-ceramic layer (DCL) La2Zr2O7/50% La2Zr2O7 + 50% 8YSZ/8YSZ was investigated. Coatings were deposited using the atmospheric plasma spraying (APS) process (ceramic layer and bond-coat) on the Ni-based superalloy substrate with Ni-22Cr-10Al-1Y bond-coat. The thickness of the ceramic top-coats in all cases were 300 m. In the case of La2Zr2O7/8YSZ, the internal sublayer was built from 8YSZ powder whereas the outer from La2Zr2O7. Between both sublayers' "composite" a 50% La2Zr2O7 + 50% 8YSZ zone was present. The "composite" 50% La2Zr2O7 + 50% 8YSZ TBC system was sprayed from two different feedstock powders with equal weight ratios. In the first part of the investigation, the microstructural characterization of the TBCs was presented. The main goals were related to the characterization of the degradation processes in different TBC systems with special emphasis on the phenomenon in the thermally grown oxide (TGO) zone related to oxidation, and the phenomenon related to phase stability in ceramic top-coats as related to temperature influence. The oxidation test was carried out in air at 1100 ffiC for 500 h. In the second step of the investigation, the numerical simulation of the monolayered TBC 8YSZ and La2Zr2O7 systems was analyzed from the stress distribution point of view. Additionally, the two-layered TBC coating of the DCL type was also analyzed.