Influence of vacuum annealing conditions on the surface oxidation and vacancy condensation in the surface of an FeAl single crystal

The influence of annealing atmosphere, temperature and time on the surface oxidation and vacancy condensation behavior of {111}-oriented single crystals of B2-type FeAl was investigated. AFM observation showed that as-annealed surfaces under a high vacuum were rugged and covered with a thin oxide film. The results obtained by TEM indicated that the thin oxide film was {001}-oriented κ-Al2O3 epitaxially grown on the {111}-oriented FeAl surface. AES measurements showed that the thickness of the oxide film was almost twice as thick as that of the passive Al2O3 film formed on the FeAl surface in an ambient atmosphere. It was found that the growth of surface mesopores is attributable to both the condensation of supersaturated vacancies in FeAl substrate and the Kirkendall effect by the surface oxidation during the vacuum annealing.