Solidification and high-temperature phase equilibria in the Fe-Al-rich part of the Fe-Al-Nb system

Partial isothermal sections of the Fe-Al-Nb phase diagram at 1000, 1170, and 1300 °C as well as the corresponding part of the liquidus surface were established experimentally for Nb contents in the range from 0 to 33 at%. This part of the phase diagram is characterized by an extended two-phase field of the (αFe) solid solution (disordered A2) or FeAl (ordered B2) with the Nb(Fe,Al)2 Laves phase. The solubility of Nb in all Fe-Al phases is small and reaches a maximum in the phase FeAl. A deep eutectic valley runs parallel to the Fe-Al axis across the large two-phase field and continues to the Al corner. The composition dependence of the eutectic temperature and the exact position of the eutectic valley on the liquidus surface including the Al-rich part were determined. The high-temperature phase equilibria are strongly affected by the liquid phase coming from the Al corner. With increasing temperature its phase field grows quickly into the ternary system resulting in a strongly reduced extension of the (αFe) + Nb(Fe,Al)2 two-phase field at 1300 °C.