Crystal and metal/oxide interface structures of nanoparticles in Fe–16Cr–0.1Ti–0.35Y2O3 ODS steel

Abstract Oxide dispersion strengthened (ODS) steel is one of the most promising candidate structural materials for the cladding of generation IV nuclear fission reactors and the blanket of future fusion reactors because it has excellent resistance to creep, irradiation, corrosion and, moreover, strong capability for managing helium due to the ultrahigh density nanometer-scale oxides. Crystal and metal/oxide interface structures of the nanoparticles in Fe–16Cr–0.1Ti–0.35Y2O3 ODS steel have been studied by high resolution transmission electron microscopy (HRTEM). The phases of 79 nanoparticles, which have diameter of 4–9 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. About 59.5% of the nanoparticles are composed of Y–Ti complex oxides. Small amount of Ti addition, i.e., 0.1 wt.%, into Fe–Cr ODS steel with 0.35 wt.% Y2O3 and, moreover, the much lower content of excess oxygen prompts the significant formation of orthorhombic and hexagonal Y2TiO5 (45.6%), instead of cubic Y2Ti2O7 (2.5%). Orthorhombic YTi2O6 (2.5%) and tetragonal YCrO4 (7.6%) oxides were firstly found in Fe–Cr–Ti–Y2O3 ODS steel. Almost all the nanoparticles are either coherent or semi-coherent with the bcc steel matrix. The crystallographic orientation correlations of the oxides and matrix were determined. The mechanisms of the formation and polymorphic transition of various kinds of oxides and, moreover, the reasons of the unusual strengthening, thermal stability and radiation tolerance of the ODS steel were discussed based on the comprehensive database developed here.