Development of advanced Fe–Al–O ODS alloy microstructure and properties due to heat treatment

Fe–Al–O ODS alloy prepared via mechanical alloying was subjected to three different heat treatments. Material basic state exhibited a fine-grained (300–500 nm) microstructure with fine dispersion of aluminum oxide particles (60% up to 20 nm). Heat treatment at 1100 °C for 3 h resulted in local grain and particles coarsening. Prolongation of the heat treatment to 24 h resulted in further grain (50 % up to 5 μm) and particle (25 % with size 25–40 nm) coarsening. Annealing at 1200 °C for 24 h led to a bimodal microstructure (35 % of grains with size 100–250 μm and 45 % of particles with size 30–60 nm) and substantial oxide particle coarsening. Microstructural changes resulted in tensile strength decrease and ductility increase. Tensile tests at 800 °C revealed a 90% decrease of tensile strength while ductility increased 4–6 times when compared to the room temperature tests. The hardening ratio was below 10 % for all the alloys and both test temperatures.