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 degrees 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 mu m) and particle (25 % with size 25-40 nm) coarsening. Annealing at 1200 degrees C for 24 h led to a bimodal microstructure (35 % of grains with size 100-250 mu m 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 degrees 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.