Revealing the chemical environment of Cr, Fe, and Ni in high temperature-ultrafine precipitate strengthened steel subjected to low fluence neutron irradiation

Abstract

• Neutron irradiated HT-UPS steel was characterized via synchrotron techniques. • Cr 23 C 6 precipitate evolution occurred at lower fluences than previously determined. • Nucleation, growth, and/or ballistic dissolution of Cr 23 C 6 at <0.3 dpa. • Atoms surrounding Fe and Ni demonstrated neutron resistance up to 0.3 dpa. High temperature-ultrafine precipitate strengthened (HT-UPS) steel has potential applications in advanced nuclear reactors as a structural material. However, little is currently known about its response to neutron irradiation. This research provides insight into the neutron irradiation-induced physicochemical changes of the major constituents in HT-UPS steels, including Fe, Cr, and Ni, using synchrotron X-ray absorption near edge structure (XANES) and diffraction. This study is the first known investigation using XANES to characterize HT-UPS steel to analyze the evolution of the atomic level chemistry. It was found that following neutron exposure, radiation-induced nucleation, growth, and/or ballistic dispersion of Cr 23 C 6 precipitates occurred at very low neutron irradiation fluences, from 0.003 displacements per atom (dpa) up to 0.3 dpa, at 600 °C, which were at least an order of magnitude lower than previous studies. Calculations of the angular momentum projected partial density of states and the XANES spectra confirmed the experimental findings of the Cr 23 C 6 precipitate evolution. In contrast, the local atomic structure around Fe and Ni atoms demonstrated irradiation resistance.