Effects of contents of Al, Zr and Ti on oxide particles in Fe–15Cr–2W–0.35Y2O3 ODS steels

Abstract

FeCrAl oxide dispersion strengthened (ODS) steel is one of the most promising candidate cladding materials of generation IV nuclear reactors because of its excellent resistance to not only corrosion but also creep and irradiation due to the ultrahigh density nanometer-scale oxides. Effects of the contents of Al, Zr and Ti on the crystal and metal/oxide interface structures of the particles in Fe–15Cr–3.7Al–2W–0.1Ti–0.6Zr–0.35Y2O3 (3.7Al–0.1Ti–0.6Zr) and Fe–15Cr–3.8Al–2W–0.12Ti–0.5Zr–0.35Y2O3 (3.8Al–0.12Ti–0.5Zr) were studied by high resolution transmission electron microscopy (HRTEM). For 3.7Al–0.1Ti–0.6Zr and 3.8Al–0.12Ti–0.5Zr ODS steels, phase identification was accomplished on 175 and 213 particles, respectively, which have peak number fraction and, therefore, represent the oxides contributing most significantly to the macroscopic properties of the ODS steels. The proportions of various types of oxides were determined. For 3.7Al–0.1Ti–0.6Zr and 3.8Al–0.12Ti–0.5Zr ODS steels, the proportions of Y–Zr complex oxides are ∼87.4% and ∼54.4% while the number fractions of Y–Al complex oxides are ∼3.5% and ∼5.2%, respectively, indicating that 0.5–0.6 wt.% Zr inhibits the formation of Y–Al complex oxides remarkably while prompts the significant occurrence of Y–Zr complex oxides. For 3.7Al–0.1Ti–0.6Zr and 3.8Al–0.12Ti–0.5Zr ODS steels, the proportions of Y–Ti complex oxides are ∼5.7% and ∼36.6%, respectively, indicating it is effective for increasing the proportion of Y–Ti complex oxides by increasing the content of Ti from 0.09 wt.% to 0.12 wt.% with the content of Zr decreased from 0.63 wt.% to 0.49 wt.%. The crystallographic orientation correlations of the oxides and matrix were determined. The formation and refinement mechanisms of oxides and, moreover, the reasons of the unusual irradiation tolerance and thermal stability of the ODS steel were discussed based on the results.