Microstructure evolution and mechanical properties of ODS FeCrAl alloys fabricated by an internal oxidation process

The fabrication of oxide dispersion strengthened (ODS) FeCrAl alloys by an innovative internal oxidation process is presented herein. The internal oxidation process for a precursor ODS FeCrAl alloy powder consists of two consecutive procedures. Active Y is segregated and enriched on the surface and grain boundaries of the ferritic powder during the first vacuum treatment. Yttrium oxide dispersoids are preferentially generated during the next oxidation treatment and become the precursors for the nanometric oxide precipitates in the subsequent hot consolidation. Nanometric Y2O3 and Y-Al-O precipitates are observed in the nominal compositions of Fe-16Cr-4.5Al-2W-0.5Ti-0.5V-0.2Y, Fe-16Cr-4.5Al-2W-0.5Ti-0.5V-0.5Y and Fe-14Cr-4.5Al-2W-0.5Ti-0.25Zr-0.8Y alloys and show a wide size distribution range from less than 10 nm to a maximum of 400 nm. No observable carbide, nitride inclusions or Al2O3 particles are identified. The improvement in the tensile strength of ODS alloys fabricated by the oxidation process is attributed to the dispersed nanometric oxide precipitates. The good ductility of the alloys is ascribed to the deficiency of ultrafine grains.