Microstructure and Mechanical Properties of a Precipitation‐Strengthened Fe–Al–Nb Alloy

Abstract

Fe–Al alloys provide an attractive property profile for applications at temperatures of up to 700 °C. Herein, a Fe–25Al–2Nb (at%) alloy is, manufactured on an application‐relevant scale. Preforms are cast and subsequently forged into a turbine blade shape. The microstructural evolution and mechanical properties, namely quasistatic strength and creep response, are tested in different manufacturing conditions and are compared to the properties of equilibrated laboratory alloys, as well as to literature results. The cast process leads to coarse‐grained initial nonequilibrium microstructures with lower amounts of Laves phase as compared to thermodynamic equilibrium. Forging at 900 °C leads to the significant formation of subgrains in the Fe–Al matrix and precipitation of the Laves phase. The as‐cast condition of Fe–25Al–2Nb exhibits a complex creep behavior governed by the transient formation of a coherent Heusler phase as well as Laves phase formation and recrystallization in later stages of creep. In the forged condition, the material behaves similarly to long‐term annealed material. Although Fe–25Al–2Nb has slightly lower strength and lower creep resistance over the entire temperature range tested, it performs well compared to Ta‐containing Fe–Al alloys due to its lower cost and density.