TEM and HRTEM study of oxide particles in an Al-alloyed high-Cr oxide dispersion strengthened steel with Zr addition

The nanoparticles in an Al-alloyed high-Cr oxide dispersion strengthened (ODS) steel with Zr addition, i.e., SOC-14 (Fe-15Cr-2W-0.1Ti-4Al-0.63Zr-0.35Y2O3), have been examined by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). Relative to an Al-alloyed high-Cr oxide ODS steel without Zr addition, i.e., SOC-9 (Fe-15.5Cr-2W-0.1Ti-4Al-0.35Y2O3), the dispersion morphology and coherency of the oxide nanoparticles in SOC-14 were significantly improved. Almost all the small nanoparticles (diameter <10 nm) in SOC-14 were found to be consistent with trigonal δ-phase Y4Zr3O12 oxides and coherent with the bcc steel matrix, with semi-coherent orthorhombic Y2TiO5 oxides occasionally detected. The large particles were mainly identified as tetragonal or cubic ZrO2 oxide. The results are compared with those of SOC-9 with a brief discussion of the mechanisms of the unusual thermal and irradiation stabilities of the oxides as well as the extraordinary corrosion resistance, excellent irradiation tolerance and superior strength of SOC-14.