The segregation of reactive elements (REs) along thermally grown oxide (TGO) grain boundaries has been associated to slower oxide growth kinetics and improved creep properties. However, the incorporation and diffusion of these elements into the TGO during oxidation of Ni alloys remains an open question. In this work, electron backscatter diffraction in transmission mode (t-EBSD) was used to investigate the microstructure of TGO within the thermal barrier coating on a Ni-based superalloy, and atom probe tomography (APT) was used to quantify the segregation behavior of REs to α-Al2O3 grain boundaries. Integrating the two techniques enables a higher level of site-specific analysis compared to the routine focused ion beam lift-out sample preparation method without t-EBSD. Needle-shaped APT specimens readily meet the thickness criterion for electron diffraction analysis. Transmission EBSD provides an immediate feedback on grain orientation and grain boundary location within the APT specimens to help target grain boundaries in the TGO. Segregation behavior of REs is discussed in terms of the grain boundary character and relative location in TGO.

We employed correlative atom probe tomography (APT) and transmission electron microscopy (TEM) to analyze the alumina scale thermally grown on the oxide dispersion-strengthened alloy MA956. Segregation of Ti and Y and associated variation in metal/oxygen stoichiometry at the grain boundaries and triple junctions of alumina were quantified and discussed with respect to the oxidation behavior of the alloy, in particular, to the formation of cation vacancies. Correlative TEM analysis was helpful to avoid building pragmatically well-looking but substantially incorrect APT reconstructions, which can result in erroneous quantification of segregating species, and highlights the need to consider ionic volumes and detection efficiency in the reconstruction routine. We also demonstrate a cost-efficient, robust, and easy-handling setup for correlative analysis based solely on commercially available components, which can be used with all conventional TEM tools without the need to modify the specimen holder assembly.