The development and stability of Y–Ti–O nanoclusters in mechanically alloyed Fe–Cr based ferritic alloys

Ferritic alloys containing a high density of nanoscale clusters of Y–Ti–O exhibit superior creep strength and potential for high resistance to radiation damage. Small angle neutron scattering (SANS) was used to characterize the sequence-of-events and the necessary ingredients for the formation of nanoclusters (NCs) during processing, as well as their thermal stability during high temperature aging. Mechanical alloying (MA) dissolves Y ₂O ₃ in the master alloy Fe–Cr–W powders. A large population of 1–2 nm NCs precipitate during subsequent high temperature consolidation. The NC sizes increase and their volume fractions and number densities decrease with increasing the consolidation temperature. Both Ti and Y are necessary for NC formation at higher temperatures. The NCs in MA957 are stable during aging at 1150 °C for times up to 243 h, but systematically coarsen at 1200 °C. The NCs coarsen rapidly and become unstable at higher aging temperatures. Variations in the alloy hardness are consistent with differences in the NC sizes and number densities.