Oxidation Behavior of Binary Aluminium-Rich Fe-Al Alloys with a Fine-Scaled, Lamellar Microstructure

The oxidation behavior of binary Fe–Al alloys with an aluminum content between 58 and 64 at.% was studied by isothermal and cyclic oxidation experiments in a temperature range of 900–1000 °C. The parabolic rate constants were determined to be comparable to those of B2-ordered Fe–48Al. All investigated alloys exhibited a fine-scaled, lamellar microstructure (<300 nm lamellar spacing), which was a result of the eutectoid decomposition of the high-temperature phase Fe5Al8 into FeAl and FeAl2. None of these two phases showed a preferential oxidation. At 900 °C θ-Al2O3 formed, whereas at 1000 °C a transformation of the initially formed θ-Al2O3 to the slower growing and passivating α-Al2O3 was confirmed by grazing incidence X-ray diffraction measurements.