Fig. 1. Microstructure and composition of TBCs.

Fig. 2. Microstructure and chemical composition analysis results for each layer of TBCs.

Fig. 3. Measurement interval and spallation life in terms of the isothermal test temperature.

Fig. 4. (a) Predicted cumulative TGOs according to the isothermal aging cycle; (b) TGO growth per cycle; open symbols represent experimental data [24].

Fig. 5. FE model and boundary conditions for the thermal stress analysis of TBCs.

Fig. 6. Layered structure of TBC observed after isothermal aging spallation test.

Fig. 7. Change in TC stress distribution after cooling from 1100 °C with the growth of TGO.

Fig. 8. Changes in the maximum stress and stress conversion phenomenon according to temperature and TGO thickness.

Fig. 9. (a) Crack generation region according to the stress conversion rate; (b) Morphologies of spallation surfaces of TBCs according to temperature; (c) Changes in the exposed BC area of the spallation surface with increasing temperature.

Fig. 10. Cumulative stress in TBCs over the isothermal aging cycle.

Fig. 11. Damage calculation using the virtual S-N curve method.

Fig. 12. Determining the suitability of virtual S-N diagram by using the isothermal aging test results.

Fig. 13. Deterioration calculation using temperature divisions [23].

Fig. 14. (a) TGO growth prediction curve in the thermal cycle test calculated through equivalent conversion; (b) Thermal fatigue stress of TBCs obtained by performing the thermal cycle test simulation and FE analysis; (c) Cumulative stress in terms of the thermal cycle; (d) Cumulative damage graph in terms of the thermal cycle.

Fig. 15. Damage accumulation of TBCs according to thermal cycle by test temperature.

Fig. 16. Prediction results of the spallation life of TBCs using the damage model and the actual test results

Fig. 17. Changes in microstructure of 7-8 wt.% YSZ TC after spallation at different temperatures: (a) 1200°C; (b) 1250°C