EBSD Observation of Micro Crack Morphologies after Thermal Exposure in Thermal Barrier Coatings(<Special Issue>Thermal Barrier Coating Systems for Gas Turbines)

Abstract

Micro-cracking process in TBCs (Thermal Barrier Coatings) due to thermal exposure was investigated using SEM (Scanning Electron Microscope) and EBSD (Electron BackScatter Diffraction) observation. Splat particle morphologies in TBCs were clearly visualized by IPF (Inverse Pole Figure) mapping. The splat structure of top coat was consisted with large granular particle region and cluster of small columnar particle region. Cracks were observed along the interfaces of large granular particle region and the cluster of small columnar particle region, along the interfaces among large granular particles and across the cluster of small columnar particles transgranularly perpendicular to columnar crystal growth direction. The onset time of extensive macro crack formation was corresponding to the Cr oxide growth at TGO (Thermally Grown Oxide) to some extent. Thus EBSD observation can be used as a powerful tool for crystallographic observation of TBC, associated with SEM and optical microscope observation.