Effects of Ce addition on the morphology, crystal and metal/oxide interface structures of nanoparticles in FeCrAl-ODS steels

Abstract

FeCrAl oxide dispersion strengthened (ODS) steel is one of the most promising candidate cladding materials in generation IV nuclear reactors due to its exceptional macro-properties. To address the stringent performance requirements of supercritical water-cooled reactors (SCPWRs), two FeCrAl-ODS steels, i.e., 3Al–0.1Ti (Fe–16Cr–3Al–0.1Ti–0.34Y₂O₃) and 2Al–0.1Ti–0.35Ce (Fe–16Cr–2Al–0.1Ti–0.35Ce–0.36Y₂O₃), were developed. This study aims to investigate how Ce addition influences the microstructure and the formation mechanisms of various oxides in ODS steels. Therefore, the grain & nanoparticle morphologies, and crystal & interface structures of nano-scale oxides of the two ODS steels were studied by transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and high-resolution transmission electron microscopy (HRTEM). The mean grain diameter of 3Al–0.1Ti and 2Al–0.1Ti–0.35Ce is 1.1 μm and 0.82 μm, respectively. Compared with 3Al–0.1Ti, the average diameter of particles of 2Al–0.1Ti–0.35Ce is relatively smaller. The results indicate that adding Ce can refine the grains and nano-sized particles. For 3Al–0.1Ti, the main particles are Y–Al–O with a proportion of ∼81.4 %. For 2Al–0.1Ti–0.35Ce, the main particles are Y–Ce and Y–Ti oxides with quantity ratios of ∼52.2 % and ∼22.1 %, respectively, while the quantity ratio of Y–Al oxides is only 12.3 %. This indicates that adding Ce can impede the occurrence of Y–Al–O while facilitating the generation of Y–Ce–O. Moreover, it is the first time that Y₂Ce₂O₇ oxide has been detected in yttria-added ODS steels with Ce. The findings obtained from this study provide key insights into the mechanisms of oxide formation & polymorphic transitions, and microstructural differences due to Ce addition. This will provide pivotal direction for the optimization of alloy compositions, promoting the innovation of ODS steels. Additionally, the feasibility analysis of the two ODS steels indicates their applicability to the SCPWR fuel cladding.