Stability of non-stoichiometric clusters in the MA957 ODS ferrtic alloy

In our past work, the commercial ferrtic oxide dispersion strengthened alloy MA957 had at least two types of nanometer-sized oxide particles: non-stoichiometric Y-, Ti-, O-enriched clusters (Y/Ti <1) and stoichiometric Y ₂Ti ₂O ₇ particle. Non-stoichiometric clusters had a much higher number density and smaller sizes than Y ₂Ti ₂O ₇ particles. Consequently, it was confirmed that the non-stoichiometric clusters dominate the oxide dispersion strengthening. This study focused on the stability and evolution mechanism of non-stoichiometric nanoclusters during annealing at 1473 K for 1 h. The annealing condition was determined considering the actual condition of consolidation processes. Characterization after the annealing showed that most non-stoichiometric Y-, Ti-, O-enriched clusters were stable, but some clusters became Y ₂Ti ₂O ₇ particles with increasing size and yttrium content. In addition, it was found that most Y ₂Ti ₂O ₇ particles contained a non-negligible content of aluminium. These particles probably coexisted together with the Y ₃Al ₅O ₁₂.