Effect of post heat treatment on thermal durability of thermal barrier coatings in thermal fatigue tests

The effects of post heat treatment and coating parameters on the microstructural development of thermal barrier coatings (TBCs) have been investigated and the thermal durability related to the microstructural evolution has been evaluated through cyclic thermal exposure tests. TBC systems with thicknesses of 2000 and 200 μm in the top and bond coats, respectively, were prepared with the air–plasma spray system using a 9 MB gun with ZrO2–8 wt.% Y2O3 (METCO 204 C-NS) for the top coat and Ni-based metallic powder (AMDRY 962) for the bond coat. The post heating was performed at a temperature of 1000 °C for 3 h with a heating rate of 5 °C/min in flowing argon (Ar) gas at 200 ml/min. The thermal exposure tests were performed with a dwell time of 60 min for 874 cycles using a specially designed apparatus—one side of the sample was exposed to a high temperature of 1100 °C and the other side was air cooled to 950 °C. The post heat treatment is an efficient process in improving the thermal durability of thick TBCs, and the TBC with porous microstructure obtained by controlling coating parameters shows a better thermal durability than those with intermediate or dense microstructures. Results indicate that post heat treatment and microstructural control are important in proposing efficient processes to improve the lifetime performance of thick TBCs in high-temperature environments.