The Oxide Dispersion Strengthened (ODS) materials are potential candidates as cladding tubes for Sodium-cooled Fast Reactors. The nano-oxides are finely dispersed within the grains and confer excellent mechanical properties to these alloys. Hence, assessing nano-particle stability under irradiation remains crucial to guarantee safe use of these materials. Although neutron irradiation remains a binding and challenging experimental study to conduct, difficulties can be overcome by ion beam processing. Ion beam processing of the ODS material allows to identify the radiation-induced Ostwald ripening as the mechanism governing the nano-particle response under irradiation. The result is the increase in size and a decrease in density of the finely dispersed Y2Ti2O7 nano-particles. Under neutron irradiation, radiation-induced Ostwald ripening appears to be less effective since a slight growth of nano-particles is observed. Further, our approach shows that nanoparticle growth kinetics should scale as φ1/3, φ being the radiation flux. This suggests that the low irradiation flux is at the origin of the slower growth kinetics of the neutron irradiated particles. Both neutron and ion irradiation induce a modification of the nanoparticles/matrix interfaces which are generally flat and sharp prior to irradiation and present steps after irradiation. This could alter the nano-particle coarsening during irradiation.

A high chromium ferritic Oxide Dispersion Strengthened steel was produced by mechanical alloying of Fe-18Cr-1W-0.3Ti-0.3Ni-0.15Si and 0.5% Y2O3 (wt.%) powders in industrial attritor, followed by hot extrusion at 1100°C. The material was characterized by Atom Probe Tomography on each step of manufacturing process: as-milled powder and in final hot extruded state. In addition, to get information on clustering kinetics the powder was also characterized after annealing at 850°C during 1 hour. Atom Probe Tomography revealed that the oxide dispersion strengthened steel Fe-18Cr contains nanometer scale yttrium- and oxygen-enriched nanoclusters in as-milled state. Their evolution is shown after subsequent annealing and hot extrusion. More well defined nanophases also enriched in Ti are observed. A mechanism of their formation is proposed. Mechanical alloying results in supersaturated solid solution with presence of small Y- and O-enriched clusters. Subsequent annealing stimulates incorporation of Ti to the nucleii that were previously formed during mechanical alloying.