Morphology, crystal and metal/oxide interface structures of nanoparticles in Fe–15Cr–2W–0.5Ti–7Al–0.4Zr–0.5Y2O3 ODS steel

Abstract The nanoparticles in a FeCrAl oxide dispersion strengthened (ODS) steel with Ti and Zr addition, i.e., UOC-10 (Fe–15Cr–2W–0.5Ti–7Al–0.4Zr–0.5Y2O3), have been examined by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The phases of 134 nanoparticles, which have diameter mainly of 4–11 nm and peak number fraction and, therefore, represent the oxides contributing most significantly to the macroscopic properties of the ODS steel, were identified and, moreover, the proportions of various types of oxides were determined. Relative to FeCrAl-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 UOC-10 were significantly improved. The nanoparticles in UOC-10 were found to be consistent with δ-phase Y4Zr3O12 (∼44.8%), defect fluorite Y2Zr2O7 (∼15.7%), perovskite YAlO3 (YAP) (∼14.2%) and orthorhombic Y2TiO5 (∼11.2%) with distorted perovskite YTiO3 oxide occasionally detected. Almost all of the nanoparticles are either coherent (∼78.4%) or semi-coherent (∼20.3%) with bcc steel matrix. The crystallographic orientation correlations of the oxides and matrix were determined. The results are compared with those of SOC-9 and SOC-14 (Fe–15Cr–2W–0.1Ti–4Al–0.63Zr–0.35Y2O3) with a brief discussion of the mechanisms of the formation of various kinds of oxides and, moreover, the unusual thermal and irradiation stabilities of the oxides as well as the excellent irradiation tolerance and superior strength of UOC-10.