Effect of Top Coat Thickness on Thermal Stability in Thermal Barrier Coatings

The microstructural evolution related to the thickness of thermal barrier coating (TBC) and their thermal stabilities have been investigated with a specific attention to defect species as well as to its morphology with the thermal exposure time. The TBCs with different thicknesses of 600 and 2,000 µm were prepared by air plasma spray (APS) process and the thermal exposure tests were performed at 950C in a furnace with a dwell time of 100 hrs till 500 hrs. The thickness of thermally grown oxide (TGO) layer in the TBC with 2,000 µm is thinner than that with 600 µm. Also, the TBC with 2,000 µm is more efficient in improving the oxidation resistance of bond coat than that with 600 µm. Vickers indentation methods are used to evaluate the interfacial stabilities. Indentation impression and crack formation of the TBC of 600 µm is easily occurred in comparison with that of 2,000 µm, showing relatively longer cracks, independent of thermal exposure. However, the crack formation and propagation through the interface does not observed in the TBC with 2,000 µm, showing crack propagation through the top coat near the interface. These results imply that the interfacial stability of TBC can be also improved with increasing the coating thickness.