Nuclear Science User Facilities 56 Si-Ni-Mn Clustering in Irradiated Fe-9Cr Oxide Dispersion Strengthend Alloy Janelle P.Wharry – Purdue University – Figure 1. Atom probe tomography (APT) reconstructed tips showing Si-Ni-Mn clustering on oxide nanoparticles in model Fe-9Cr irradiated with (a) 5 MeV Fe++, 100 dpa, 400°C, (b) 2 MeV protons, 3 dpa, 500°C, and (c) neutrons in ATR, 3 dpa, 500°C. Oxide dispersion strengthened (ODS) alloys are nanofea- tured materials, having grains of diameter ~250 nm and containing a dispersion of oxide nanoparticles. The fine grains and oxide nanopar- ticles provide the alloy with high strength at elevated temperatures and dimensional stability under irra- diation, making ODS alloys leading candidates for structural components in fusion and advanced fission reac- tors. Most post-irradiation evaluation (PIE) experiments of ODS alloys have focused on evaluating the stability of the oxide nanoparticles and several researchers have observed instability of these nanoparticles under irra- diation at moderate temperatures. However, there have been no specific investigations into the clustering of Si, Ni, and Mn in ODS alloys.These minor elements have been found to cluster readily in other b.c.c. Fe‑Cr alloys, including commercial ferritic/ martensitic (F/M) steels. Since ODS steels are based upon the b.c.c. Fe‑Cr alloy system, it is unsurprising that Si, Ni, and Mn would also cluster in ODS alloys. Project Description The objective of this project is to understand the role of Si, Ni, and Mn clustering in irradiated ODS alloys. Specifically, we test the hypothesis that there is a co-evolution of Si-Ni-Mn rich clusters (which nucleate under irradiation) and pre‑exisitng oxide nanoclusters under irradiation. In this project, we first conducted proton and Fe2+ self‑ion irradiations to several doses between 1 and 100 displacements per atom (dpa) at 500°C on a model Fe-9Cr ODS alloy. We also access a 3 dpa, 500°C neutron irradiated specimen of the same alloy heat through the NSUF Nuclear Fuels and Materials Library.We carried out microstructure characterization by atom probe tomography (APT) for the nanoscale cluster analysis, along with complementary transmission electron microscopy (TEM) to characterize dislocations, loops, carbide