Atom probe tomography of thermally grown oxide scale on FeCrAl

Thermally grown Al₂O₃ scales formed on a FeCrAl alloy were successfully analyzed using pulsed green laser atom probe tomography. Two types of atom probe tomography specimens, the "thin oxide" type: a thin Al₂O₃ layer (<100 nm) with underlying metal (1 μm), and the "thick oxide" type: only with Al₂O₃ (1 μm), were prepared and analyzed. It was found that the thin oxide type yields poorer mass resolution due to a combined effect of laser absorption and thermal conduction effects. Application of a relatively low laser energy yields a better mass resolution and increased multiple events, however, more accurate quantification results. Although no other oxide phase than Al₂O₃ is expected to form, some iron-oxygen and chromium-oxygen molecular ions were recorded at the Al₂O₃/metal interface due to the large change in evaporation field over this zone.