This project aims to quantify the impact of as-printed heterogeneity in laser powder bed fusion (LPBF) 316LSS on spatially dependent post-irradiation segregation and precipitation behavior. To accomplish this task, the research team proposes to use the Low Activation Materials Development and Analysis (LAMDA) lab at ORNL to perform site-specific nanoindentation on varying weld pool regions of neutron irradiated samples. targeted focused ion beam (FIB) liftouts, followed by on-zone scanning transmission electron microscopy (STEM) with coupled energy dispersive X-ray spectroscopy (EDS). The samples to be investigated were previously irradiated to 0.2 and 2 displacements per atom at a target irradiation temperature of 300°C in the High Flux Isotope Reactor (HFIR) and are readily available for the targeted microscopy and indentation proposed in this work. Due to the immediate availability of specimens, and existing repository of pre-irradiation specimen data available through the previous Transformational Challenge Reactor (TCR) program, only 2-weeks of instrument time is requested at the LAMDA facility. This work is expected to be completed within 3 months of the project award date, with plans for a publication disseminating project results. From the coupled STEM+EDS and nanoindentation results, the research team will identify how nanoscale features, including dislocation cellular structures, loops, and precipitate densities relate to nano hardness results in regions with observed heterogeneity. This project is particularly impactful since it is the first study on how intrinsic heterogeneity at the microstructure level in additively manufactured 316LSS parts may impact post-irradiation performance. If significant deviations in post-irradiation evolution are observed, any standard material qualification approaches may need revision as spatial variation in mechanical performance may need to be considered prior to part qualification.

The mission of the DOE Office of Nuclear Energy is to advance nuclear power to meet the nation's energy, environmental, and national security needs. One key aspect required to achieve this mission is to enable the rapid qualification of the materials and/or processes needed to build the next generation of nuclear reactors. This RTE focuses on the quantification of how heterogeneities induced from modern manufacturing processes affect the evolution of defect structures in additively manufactured steels. The topics in this proposal align well with the mission of relevant programs, including the DOE NE Advanced Materials & Manufacturing Technologies (AMMT) program and the DOE NE Advanced Fuels Campaign (AFC), which are programs aimed at rapidly developing and deploying structural and core materials for nuclear reactor concepts, respectively. Unfortunately, the use of modern manufacturing methods like laser powder bed fusion (LPBF) commonly results in significant variations in the starting microstructure and chemical composition throughout printed parts. This work will provide unique but synergistic data to previous PIE data funded under the Transformational Challenge Reactor (TCR) irradiation campaign of 316L samples produced via LPBF. Therefore, the post-irradiation data that will be collected in this work will, for the first time, reveal whether microstructural heterogeneities induced during LPBF need to be taken into consideration in accelerated nuclear material qualification frameworks. This outcome will thus provide a roadmap for future programmatic PIE efforts in programs such as AMMT that are focused on accelerated qualification of a variety of structural materials for advanced reactor applications.