Microstructure and Phase Transformation Temperatures of Two-Phase FeAl (B2) + FeAl_2 Alloys

摘要

Fe-Al alloys with about 55 to 65 at.% Al undergo a eutectoid transformation at 1095 °C: Fe_5Al_8 (ε) <-> FeAl + FeAl_2. Hence, as-cast Fe-Al alloys in this composition range show a very fine-scaled lamellar microstructure (average lamellar spacing below 500 nm) consisting of the two phases FeAl and FeAl_2. The microstructure looks similar to the α_2 + γ lamellar microstructure of Ti-Al-based alloys, which is known for having well-balanced properties in terms of creep, ductility and strength. However, there is limited knowledge about the properties of Fe-Al-based alloys in this composition range. In this study, a series of as-cast as well as heat-treated Fe-Al alloys with compositions between 57 and 63 at.% Al were investigated. The microstructures and crystal structures were analysed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The composition dependence of all transition temperatures was obtained by differential thermal analysis (DTA).