Abstract
The morphology and composition of the thermally grown oxide (TGO) layer in a thermal barrier system with a NiCoCrAlY bond coat are characterized by a combination of scanning and transmission electron microscopy, focused ion beam sectioning and energy-dispersive spectroscopy (EDS) element mapping. The investigation has revealed a complex TGO that exhibits numerous thickness inhomogeneities (‘pegs’), and a sizable distribution of nano-scale second phase particles. These particles have been determined to be of two types: regions of entrained bond coat and oxides based on Y 2O 3 and HfO 2. The most probable phase makeup of the oxides is a cubic fluorite of approximate composition 4HfO 2–Y 2O 3. Diffusion of Hf and Y from the bond coat or entrapment of bond coat elements during TGO growth are the most likely mechanisms for the formation of these oxide particles.
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