The effect of oxide scale roughness on the plasticity of iron aluminide alloy

Iron aluminides based on the stoichiometric compositions of Fe3Al and FeAl exhibit poor room temperature ductility due to environmental embrittlement. The embrittling agent is hydrogen liberated from water vapour in contact with an aluminium-rich surface. The formation of Al2O3 oxide scale can act as a barrier retarding the hydrogen penetration from the atmosphere inside the alloy. This barrier effectiveness depends on the scale surface roughness caused by the formation of Al2O3 whiskers. This paper presents a way to suppress the growth of these whiskers. The application of a two-stage isothermal oxidation enabled creating at a lower temperature an intermediate layer, consisting of metastable γ and θ oxides, which contributed to the limitation of α-Al2O3 oxide whiskers growth at a higher temperature and this way to reducing the scale roughness. It has been found that a decreased roughness of scale surface has a favourable influence on iron aluminide plasticity at room temperature.