Microtexture analysis of the alumina scale in thermal barrier coatings

Transmission electron microscopy-based grain orientation mapping method was employed to investigate the microtexture of the alumina scale formed in commercial thermal barrier coatings (TBCs) with two standard types of Pt-enriched bond coats. Reliable orientation/phase maps with a spatial resolution down to 2 nm were acquired on the alumina grains. It was observed that the alumina scale on the Pt-aluminide β-phase bond coat has a stronger c-axis texture normal to the bond coat surface, in comparison with that on the Pt-diffused γ/γ′-phase bond coat. The microtexture of the alumina scale could affect its effective coefficient of thermal expansion, which is a contributor to the severity of the bond coat rumpling mechanism of TBCs failure.