Collaborative Research: Determination of Ni-Fe-Cr Species Dependent Transport Through Control of Temperature, Irradiation, and Grain Size

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TECHNICAL SUMMARY: Ni-Fe-Cr based fcc alloys (e.g., Ni-based and austenitic steel alloys) are frequently used as structural materials in a wide range of technologies, including nuclear reactors. Many aspects of Ni-Fe-Cr alloy microstructural evolution, particularly under irradiation, are controlled by point defect transport with species dependencies that are still poorly understood. In this project a novel approach to determine the species-dependent diffusion coefficients in Ni-Fe-Cr steel alloys is proposed. It is based on measurements and modeling of Radiation Induced Segregation (RIS) of nanocrystalline materials. The proposed work integrates multiple approaches to understanding point defect transport in Ni-Fe-Cr and to RIS, including grain size control, RIS characterization tools (STEM-EDS, Focused Ion Beam, TEM, and Atom Probe tomography), and multiscale ab initio based models (including cluster expansion, kinetic Monte Carlo and rate theory modeling). The work will provide a new level of insight into the magnitude and mechanisms of Ni-Fe-Cr species-dependent transport and inform future microstructural modeling.NON-TECHNICAL SUMMARY: Ni-Fe-Cr based steels are frequently used as structural materials in a wide range of technologies, including nuclear reactors. Essential aspects of the long-term reliability of these steels, particularly under irradiation, are controlled by aspects of Ni, Fe, and Cr diffusion that are still poorly understood. The PIs propose to integrate tools from materials nanotechnology and molecular-scale computer simulation to provide new levels of insight into how Ni, Fe, and Cr are transported in these steels under extreme conditions. The results will be integrated into higher levels models that aid in the prediction of steel reliability and the development of new materials. This project will train graduate students and postdoctoral researchers to work on a multi-location team and in fundamental areas of materials characterization, modeling, and their interaction. This work will also further the involvement by some of the investigators in the Women in Nuclear Science (WINS) organization and activities at the Advanced Test Reactor National Scientific User Facility (NSUF).