Nanoclustering in a MA/ODS Ferritic Alloy

A new higher chromium variant of mechanically alloyed (MA) oxide dispersion strengthened (ODS) ferritic alloy, designated 14YWT, has been developed. The microstructures of this alloy have been characterized in the local electrode atom probe from the initial ball milled flakes through the extruded material that was heat treated at up to 1380degC. No nanoclusters were found in the ball milled flakes but some layering of yttrium and oxygen was observed. A high number density of Ti-, Y- and O-enriched nanoclusters was observed in the flakes after a simulated extrusion treatment of 1 h at 850degC. The nanoclusters were also observed after annealing an extruded rod for 1 h at 1380degC and the grain boundaries were found to be enriched in chromium and tungsten. Results of first-principles calculations on oxygen binding energy in the presence of vacancies suggest that the condition for stable nanoclusters is a well-dispersed Y distribution with more Ti than Y