Additive manufacturing offers the possibility of geometries unrealizable through conventional manufacturing methods. The microstructure imparted through the rapid solidification of the AM process creates a network of entangled dislocations. Based on prior work in irradiated stainless steels, dislocations likely serve as nucleation sites for embrittling Ni-Si(Mn) clusters. The degree of radiation hardening and impact on yield strength is strongly correlated to the size, density, and composition of Ni-Si clusters in irradiated austenitic stainless steels. Heat treatments prior to irradiation to relieve internal stresses or remove the initial dislocation network may delay the onset of nanocluster nucleation by relying on the formation of dislocation loops to act as preferential nucleation sites. The objective of this work is to evaluate the effectiveness of thermal processing on the co-location of solute clusters and dislocations in additively manufactured 316L stainless steel. We hypothesize that the initial dislocation cell microstructure imparted by the rapid solidification in an as-printed AM steel will serve as preferential nucleation sites for Ni-Si(Mn) clustering, resulting in a higher density of nanometer sized clusters compared to dislocation loops as nucleation sites in a solution annealed or stress-relieved condition. Therefore, we propose to use atom probe tomography to determine the size, density, composition, and likely co-location of solute clusters with dislocations in HFIR irradiated additively manufactured 316L stainless steel as a function of irradiation temperature from 376°C up to 600°C and processing conditions with a wrought 316L as a control. The proposing team seeks use, through the Nuclear Science User Facilities, of the Cameca LEAP 4000X HR at the Center for Advanced Energy Studies (CAES) for characterization of dislocation loops, dislocation cells, and the distribution of solutes on them with support at the LAMDA laboratory for sample preparation. APT needle tips will be prepared in bulk form using the Versa SEM/FIB in LAMDA with the final thinning to be conducted using the Quanta SEM/FIB at CAES. The APT data collection and analysis conducted in accordance with best practices established for Ni-Si cluster analysis in steels. The data will be analyzed using radial distribution functions, frequency distribution analysis using Pearson correlation coefficients, maximum separation method, and isosurface maps to determine the spatial relationship between enrichments of Si, Ni, and Mn with dislocations according to best practices for each method. The availability of this dataset will support ongoing development activities in determining the processing of additively manufactured 316 stainless steel for advanced reactor applications.

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. This RTE focuses on the generation of data related to the co-location of dislocations and solute clusters for several heat treatments of irradiated additively manufactured 316L stainless steel at three temperatures relevant to advanced nuclear reactors. Demonstration of the processing and resulting cluster evolution would directly benefit the DOE-Office of Nuclear Energy (NE) and advanced manufacturing R&D communities, including DOE-EERE and AMO programs. The objectives of this proposal align strongly with the DOE NE Advanced Materials & Manufacturing Technologies (AMMT) program mission to develop cross cutting technologies and to accelerate the development, qualification, demonstration and deployment of materials and manufacturing technologies to enable reliable and economical nuclear energy. While not directly implicated with this RTE, the focus on 316L stainless steel and the mechanistic understanding of the co-evolution of dislocation loops and solute clusters may also be of interest to the Light Water Reactor Sustainability (LWRS) program.