Characterization of mechanically alloyed powders for high-Cr oxide dispersion strengthened ferritic steel

High-Cr oxide dispersion strengthened (ODS) ferritic steel powders with the nominal composition of Fe-16Cr-4Al-0.1Ti-0.35Y₂O₃ in wt% were produced by milling of elemental powders and Y₂O₃ particles in argon atmosphere to investigate changes in the particle properties during mechanical alloying (MA). SEM observation and PSD analysis revealed that the MA powders milled for different times were composed of agglomerated particles having multimodal distributions with substantial size variation ranging from several μm to 350 μm. The mean size of particles rapidly increased at the initial stage of MA, then gradually decreased to 22 μm with increasing milling time up to 48 h, and kept constant thereafter. During milling of the Fe-16Cr-4Al-0.1Ti-0.35Y₂O₃ powder, MA within 6 h had mainly taken place between Fe and Al to form a bcc-Fe(Al) solid solution. The lattice constant of bcc-Fe steadily increased with a drastic increase in the solute concentrations of Cr, Al, and Ti in Fe. Alloying between Fe and alloying elements is almost fulfilled after milling for 48 h. The MA powder milled in air was much smaller than that milled in gaseous argon under the same conditions. Milling in an air atmosphere is effective to reduce the particle size of the ODS ferritic steel powder, although the pickup of oxygen from environment causes too high excess oxygen content.