Multiscale Modeling of Discontinuous Precipitation in U-Nb

Abstract

Discontinuous precipitation (DP) was experimentally observed in the uranium-niobium nuclear fuel. The reaction is undesirable as it degrades the fuel’s corrosion resistance and ductility. To minimize the impacts, it is important to understand the fundamental thermodynamics and kinetics of DP. In this work, we proposed to study the microstructure evolution of DP using a multiscale approach. In particular, three combinatorial methodologies including (1) first-principles calculations, (2) CALPHAD and (3) phase-field modeling were practiced. Initially, first-principle calculations were carried out to calculate for the ground-state formation energy of U-Nb’s bcc phase. The ab initio energetic data were then used in CALPHAD assessment to achieve for a self-consistent thermodynamic description of U-Nb system. Next, atomic mobilities and diffusivities of the bcc phase was estimated also in the framework of CALPHAD. Finally, phase-field simulation was carried out to model the microstructure evolution of DP’s lamellae, using the achieved thermodynamic and kinetic information. Results show good agreements with experiments.