Pyramidal Structures on Yttria‐Stabilized Zirconia after High Temperature Exposure at 1500°C: New Features on an Old Material

For several decades, yttria‐stabilized zirconia (YSZ) has been the state‐of‐the‐art material for thermal barrier coatings (TBCs), e.g., in gas turbines, for temperatures up to 1200°C. At higher temperatures, the YSZ undergoes detrimental phase transformations and strong sintering, which leads to early failure of the TBC system. Recently, it was shown that this early failure is correlated to the exact cooling rate applied. It was shown that the lifetime of a TBC system tested in a burner rig at 1550°C was not reduced, when the cooling rates were reduced strongly, e.g., to 10 K/s. In the present study, a new, not yet in the literature reported, pyramidal topography was detected in YSZ samples being cycled at about 1550°C. Analyses were performed using scanning electron microscopy and also transmission electron microscopy. The pyramidal structures were present immediately after preparation of cross sections and increased in amount and size during storage at room temperature in laboratory air.