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Nuclear Science User Facilities 106 Microstructural and Mechanical Characterization of Self-Ion Irradiated 14LMT Nanostructured Ferritic Steel Indrajit Charit University of Idaho icharituidaho.edu Advanced reactors need high- performance materials to serve under harsh conditions such as higher temperature higher radia- tion doses and extremely corrosive environments. Nanostructured ferritic steels NFS are such a class of mate- rials.They are produced by mechanical alloying MA of the elemental or pre-alloyed metallic powder typically incorporating nanosized yttria Y2O3 powder followed by a traditional consolidation process such as hot extrusion or hot isostatic pressing HIP. NFS have excellent potential for advanced fuel cladding and structural materials applications in fast reactors. Project Description Since neutron irradiation is out of the scope of this RapidTurnaround Experiment RTE the aim of the project is to investigate a new NFS known as 14LMT Fe-14Cr-1Ti- 0.3Mo-0.5La2O3 wt. that was recently developed by this research group and other collaborators. Samples were irradiated at doses up to 100 displacements per atom dpa and relevant microstructural charac- terization and mechanical properties evaluations were performed. Titanium is generally added toY2O3 to form complex yttria-titanium-oxygen Y-Ti-O-based particles in order to make the dispersed oxides much finer and stable at elevated temperatures. The 14LMT alloy uses lanthana La2O3 instead of the traditionalY2O3. Spark plasma sintering SPS was used to consolidate the mechanically alloyed powder. NFS performance is largely determined by the ultra-high number density of nanosized oxide particles dispersed throughout the microstructure.These nanofeatures are stable at high tempera- tures and are expected to impart excel- lent high-temperature strength and irradiation stability to NFS.This work could lead to the development of high- performance fuel cladding materials for advanced fast reactors. Accomplishments The stability of nanoclusters in NFS under irradiation is critical. Collision cascades can eject solute atoms from them and change their physical char- acteristics. In order to understand their stability the lanthana-bearing 14LMT alloy was exposed to self-ion Fe2 irradiation at both room temperature 30C and elevated temperature 500C as a function of ion dose at 10 50 and 100 dpa. Subsequently the irradiated material was characterized by transmission electron microscopy TEM for microstructural character- istics atom probe tomography APT for nanocluster sizecompositional analyses and nanoindentation to measure hardness. Overall morphology and number density of the nanofeatures remained largely unchanged after irradiation. The average radius of the nanofeatures in the sample irradiated at 500C100 dpa was slightly reduced.A notable level of irradiation hardening and enhanced dislocation activity occurred after ion irradiation except at 30C and 50 dpa. Other microstructural features such as grain boundaries and a high density of dislocations also provided defect sinks to assist in defect removal. A comprehensive paper based on this work is under review with the Journal of Nuclear Materials. Future Activities While this project has been completed a new RTE project Microstructural and Nanomechanical Characterization of a Lanthana-Bearing Nanostructured Ferritic Steel Irradi- ated with High Dose Iron Ions has recently been approved.This will allow the project team to continue its work on understanding ion-irradiation response of 14LMT to higher dose levels up to 400 dpa. This work could lead to the development of high-performance fuel cladding materials for advanced fast reactors.