Degradation in a Thermal Barrier Coating

The failure of a thermal barrier coating involves cracking and spalling of the ceramic layer, primarily brought about by bond-coat oxidation during operation. The present investigation focuses on the microstructural and microchemical changes in a thermal barrier coating, oxidized in air for 1 and 10 h at 900{degree}C. The zirconia coating shows a gradual increase in the amount of monoclinic phase with time at temperature. The bond-coat layer shows substantial aluminum depletion in the region adjacent to the ceramic. This aluminum forms an oxide layer (Al{sub 2}O{sub 3}) at the interface. However, nickel oxide (NiO) is also found to be another important oxidation product. The relevance of these observations to the degradation observed in thermal barrier coatings is discussed.