Atom Probe Tomography at Karlsruhe Nano Micro Facility at KIT Germany – Tomasz Stasiak

Title: Investigation of nanometric oxide precipitates and phase separation in FeCrAl-Y2O3 oxide dispersion strengthened alloys with the addition of Ti and V after annealing at 475 °C for 1000 h

Abstract: FeCrAl oxide dispersion strengthened (ODS) alloys are promising materials for the nuclear industry. Nanometric oxide precipitates homogeneously distributed in the matrix are the primary source of exceptional properties of these alloys. Nanometric oxides act as sinks for irradiation-induced defects. Thus, they significantly increase the irradiation resistance. Moreover, nanometric precipitates significantly increase mechanical strength. One of the problems of FeCrAl ODS alloys is the embrittlement that occurs after prolonged exposure at temperatures near 475 °C (so-called 475 °C embrittlement). It is the effect of the separation at the nanometric scale of the bcc matrix phase into Fe-rich (α) and Cr-rich (α’) phases. Two compositions of FeCrAl-based ODS with the addition of Y2O3, Ti, and V have been studied. The only difference between the two investigated alloys is the content of vanadium, which can significantly improve mechanical properties. The samples were produced using the powder metallurgy technique. Subsequently, the annealing at 475 °C for 1000 h was performed to evaluate the susceptibility to 475 °C embrittlement.

The aim of the project is to characterize the chemical composition of nanometric oxide precipitates in two FeCrAl-based ODS alloys using atom probe tomography (APT). The TEM-EDS studies were performed to characterize oxides; however, we hope that using APT will make the characterization of the smallest oxides more precise. Moreover, APT investigations should help evaluate microstructural evolution after aging at 475 °C for 1000 h. The mechanical properties investigations revealed different behaviors in the samples depending on the vanadium content. After aging, the vanadium-free sample is more brittle than the vanadium-containing sample. Therefore, it can be suggested that during the aging, the nanometric brittle Cr-rich phase formed in the vanadium-free sample. However, the conducted TEM and TEM-EDS investigation could not unambiguously confirm that. We hope that by using APT, we will be able to verify the presence of a nanometric Cr-rich phase in the sample.