| Summary: | A FIB/STEM interfacial study was performed on a TBC/Ti<sub>2</sub>AlC MAX phase system, oxidized in an aggressive burner rig test (Mach 0.3 at 1300 °C for 500 h). The 7YSZ TBC, α-Al<sub>2</sub>O<sub>3</sub> TGO, and MAXthal 211<sup>TM</sup> Ti<sub>2</sub>AlC base were variously characterized by TEM/STEM, EDS, SADP, and HRTEM. The YSZ was a mix of “clean” featureless and “faulted” high contrast grains. The latter exhibited ferro-elastic domains of high Y content tetragonal <b>t″</b> variants. No martensite was observed. The TGO was essentially a duplex α-Al<sub>2</sub>O<sub>3</sub> structure of inner columnar plus outer equiaxed grains. It maintained a perfectly intact, clean interface with the Ti<sub>2</sub>AlC substrate. The Ti<sub>2</sub>AlC substrate exhibited no interfacial Al-depletion zone but, rather, numerous faults along the basal plane of the hexagonal structure. These are believed to offer a means of depleting Al by forming crystallographic, low-Al planar defects, proposed as Ti<sub>2.5</sub>AlC<sub>1.5</sub>. These characterizations support and augment prior optical, SEM, and XRD findings that demonstrated remarkable durability for the YSZ/Ti<sub>2</sub>AlC MAX phase system in aggressive burner tests.
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