Strain Development in Oxide Scale during Phase Transformation of FeO

Development of a strain in oxide scale during phase transformation of FeO was investigated by a flexure method. A pure iron foil was oxidized on only one side, and the formed FeO was transformed at 400 or 500 degrees C. In-situ observation of the bending behavior of the foil-formed specimen during the phase transformation of FeO was performed. Compressive strain develops in the scale in the early stage of the phase transformation, following which a significantly large expansion strain develops. Such a strain development corresponds to the two-step phase transformation of FeO and can be explained by the volume change of the scale considering the non-stoichiometry of FeO.