Evaluation of stress concentrations during high-temperature exposure on the lifetime of single and dual-layer ZrO2-8Y2O3/ZrO2-9.5Y2O3-5.6Yb2O3-5.2Gd2O3 TBCs

In this study, the effective stresses in determining the lifetime of new-generation single-layer ZrO2-9.5Y(2)O(3)-5.6Yb(2)O(3)-5.2Gd(2)O(3) (ZGdYbYO) and dual-layer ZrO2-8Y(2)O(3) (YSZ)/ZGdYbYO thermal barrier coatings (TBCs) were investigated. For this purpose, single-layer ZGdYbYO and dual-layer YSZ/ZGdYbYO TBCs were applied on IN738LC/CoNiCrAlY by atmospheric plasma spraying technique. Then, their cyclic oxidation behavior was studied at 1100 degrees C with 4-h cycles. The morphologies of the TBCs (before and after oxidation) were investigated by field emission scanning electron microscopy ( FESEM). In addition, the mechanical behavior of the TBCs was examined by the nano- indentation test. Thermal stress was measured in single-layer ZGdYbYO and dual-layer YSZ/ZGdYbYO TBCs to be 1.2 and 1.1 GPa, respectively, with thermal growth oxide (TGO) layer growth causing stresses of 0.8 GPa and 0.3 GPa, respectively. The variation in the energy release rate of the TBCs during oxidation cycles was calculated. The results showed that the changes in the energy release rate of duallayer YSZ/ZGdYbYO TBC compared to single-layer ZGdYbYO TBC are less, and, therefore, have a better high-temperature performance. Applying an intermediate YSZ layer with higher fracture toughness than that of ZGdYbYO between the bond and top coats enhances the mechanical properties of new TBCs and extends their lifetime by improving their resistance to high-temperature oxidation.

Automated summary

In this study, the effective stresses in determining the lifetime of new-generation thermal barrier coatings (TBCs) were investigated. It was found that the dual-layer YSZ/ZGdYbYO TBC exhibited better high-temperature performance compared to the single-layer ZGdYbYO TBC, with minimal variation in energy release rate. The use of an intermediate YSZ layer between the bond and top coats improved the mechanical properties and resistance to high-temperature oxidation of the TBCs.