Microstructural changes occur in thermal barrier coating (TBC) under high temperatures oxidizing atmosphere. Thermally grown oxide (TGO) grows at the interface between topcoat and bondcoat and sintering of topcoat proceeds. The influence of microstructural changes on the crack growth in the topcoat is investigated in analytical and experimental methods. The stress states in the topcoat with TGO growth is examined by finite element method (FEM), focusing on the cooling process of the thermal cycling under temperature gradient. It suggests that the TGO less than 10μm does not give remarkable influence on the stress distribution in topcoat except in the vicinity of the interface. Furthermore, TBC specimens are subject to thermal aging at high temperature in air in order that the microstructural change occurs, and subsequent thermal cycling tests under temperature gradient are also carried out using plasma gas. The analytical and experimental results indicate that TGO less than 7μm does not give remarkable influence on the crack growth in topcoat except in the vicinity of the interface, and suggest that sintering of the topcoat during thermal aging increases the resistance to crack growth.

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