Control of Kinetic Processes in Irradiated Alloys through Compositional Patterning

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TECHNICAL: The advanced energy systems push operating environments to more severe and aggressive extremes, including high temperature, high radiation dose, and high mechanical stresses. A new generation of materials is required to meet these challenges since current materials, which were designed using knowledge developed as long as 50 years ago, will not operate safely, reliably, and economically under these conditions. This program explores a fundamentally new approach for the design of materials that would permanently resist radiation. PIs plan a new approach whereby alloy microstructures are designed to include a high density of point-defect traps that are dynamically stable under irradiation. This goal is achieved by taking advantage of PIs? past work on nanoscale compositional patterning induced by irradiation, and learning how to use these compositional heterogeneities as effective traps for point defects. By design, the nanostructured materials would thus be radiation-insensitive. PIs plan to apply this approach to selected Cu-base and Fe-base model alloys, as well as to similar alloys strengthened by nanoscale oxide dispersion. In the latter case, nanocomposite oxide-metal thin films are grown by combining cluster beam deposition with magnetron sputtering. The thin films are characterized before and after ion irradiation with a combination of techniques, including XRD, TEM, and atom probe tomography. A particular emphasis is put on the latter since it achieves sub-nanometric chemical resolution in three dimensions, and thus makes it possible to fully characterize nanostructured compositional patterns. The point-defect trapping efficiency of these nanostructures is assessed by radiation-enhanced diffusion and swelling measurements. A computational effort would identify the conditions for compositional patterns to remain dynamically stable even as the microstructure is slowly drifting. To achieve this goal, in collaboration with Lawrence Livermore National Laboratory, PIs will implement a new parallel kinetic Monte Carlo algorithm that speeds up simulations by several orders of magnitude, thus making it possible to follow the complex evolution of the microstructure in the simulations. NON-TECHNICAL: The research has broad scientific impact for the development of alloy design strategies for new materials that are critical to advanced energy production systems. Besides publishing widely the results from this research, PIs plan to organize, in the US, a summer school on Materials under Irradiation. The objective is to educate the next generation of scientists and engineers required to maintain or even expand the share of nuclear energy in the US energy production portfolio. In addition, the two graduate students working on this project will be trained on the most advanced instruments of materials characterization. PIs will hire undergraduate assistants, in particular women and underrepresented minorities. The present work will be integrated into the PIs teaching activities, exposing undergraduate students to the potentials and the challenges offered by nanostructured materials. PIs will also expand ?Materials Mobile? high-school visit program so as to reach a much larger student population.