XAFS and TEM studies of the structural evolution of yttrium-enriched oxides in nanostructured ferritic alloys fabricated by a powder metallurgy process

Abstract The speciation and structural evolution of nanoscale yttrium-enriched oxides in numerous reduced activation oxide dispersion strengthened (ODS) ferritic steels have been investigated by X-ray absorption fine structure (XAFS) spectroscopy (including X-ray absorption near-edge structure and extended X-ray absorption fine structure) and transmission electron microscopy (TEM). The local structure and speciation of Y-enriched oxides during the fabrication process have been traced by Yttrium (Y) K-edge XAFS in fluorescence mode for both mechanical alloyed (MA) powders and compacted ODS alloys. After 24 h of milling, only 10%–14% of the initially added 0.3 wt. % Y 2 O 3 dissolves into the steel matrix and titanium (Ti) exhibits a minor influence on the Y solid solution during the MA. The EXAFS analysis for compacted ODS alloys indicates the formation of new Y-enriched oxides rather than initial Y 2 O 3 . The presence of Y–Cr–O/Y 2 O 3 has been confirmed by EXAFS and energy dispersed X-ray spectroscopy (EDX) elemental mapping in the compacted ODS alloy without Ti, while Y–Ti–O/Y 2 O 3 was observed in Ti-containing (0.2–0.4 wt. %) ODS alloys. The addition of Ti exhibits an evident influence on the consolidation process rather than in the MA.