Life approximation of thermal barrier coatings via quantitative microstructural analysis

The durability of thermal barrier coatings (TBCs) can dictate the life of the hot section engine components on which they are applied. In this study, we examine the microstructural degradation of air plasma sprayed ZrO2-8 wt.% Y2O3 TBCs with a low-pressure plasma sprayed CoNiCrAlY bond coat on an IN 738LC superalloy substrate. Thermal cyclic tests were carried out in air at 1100 °C with a 1-, 10-, and 50-h dwell period, proceeded by a 10-min heat-up and followed by a 10-min forced-air-quench. Microstructural analyses were carried out to document the growth of the thermally grown oxide scale, the depletion of the Al-rich β-NiAl phase in the bond coat, and the population and growth of micro-cracks near the YSZ/bond coat interface. Evolution in these microstructural features was examined with respect to the lifetime of TBCs. A lifetime approximation model was developed, via modification of Paris Law, based on the experimental data. The model predicted the TBC lifetime within 10% of the experimental lifetime.