First Principles-based Thermokinetic Modeling of Steels and Nickel Alloys for Nuclear Applications.

摘要

The objective of this dissertation was to develop multiscale modeling frameworks for describing modes of thermal and radiation-induced degradation in steels and Ni alloys for nuclear applications. The development of these models was performed according to the following general method: first, electronic structure calculations were performed to obtain key atomistic energies and insights. These calculations then formed a foundation for atomistic simulations and continuum level models used to describe microstructural processes of interest. The results of these models were compared to experimental measurements, and used to identify the fundamental mechanisms underlying the observed material phenomena.;This approach was applied to three distinct topics. The first is the theory and prediction of radiation induced segregation in the Ni-Cr and Fe-Cr systems. In this subproject, the modeling effort yielded an important new understanding of the role of interstitial diffusion in radiation induced segregation. The effects of defect annihilation kinetics at grain boundaries were also examined. The second topic was the kinetics of the disorder-order phase transformation in Ni-Cr alloys. This project resulted in a physics-based model for describing the phase transformation that shows good agreement with both atomistic simulations and experimental measurements. The predictions of this model indicate that this phase transformation may be of serious concern in Ni-Cr alloys near the Ni2Cr stoichiometry during very long service lifetimes. Finally, the third topic was the evolution of oxide nanoprecipitates in nanostructured ferritic alloys. The key results of this effort were a better understanding of nanoprecipitate coarsening mechanisms and the effects of alloy composition on nanoprecipitate size distribution. The predictions of this model also indicate that the nanoprecipitates in nanostructured ferritic alloys should be thermally stable for as long as 80 years at proposed operating temperatures. In all three projects the first principles-based foundation provided by the electronic structure calculations allowed the resulting models to go beyond empirical fitting, and to provide understanding of the mechanisms underlying the microstructural processes of interest.