Stability of β-Nb phase in Zr–Nb alloys under neutron irradiation: Phase field modeling

Abstract

A phase field approach to study stability of β-Nb precipitates in Zr–Nb alloys is extended by taking into account local rearrangement of point defects and misfit dislocations. Kinetic properties of β-Nb phase formation are discussed at a heat treatment stage. Stability of secondary phase precipitates is studied at different irradiation temperatures and dose rates. It is shown that processes of dissolution/growth of precipitates are governed by the competition of ballistic mixing and thermal diffusion. It is found that at large values of dose rates and low temperatures, precipitates are dissolved due to a major role of ballistic mixing, whereas at low dose rate and elevated temperatures, β-niobium particles grow slowly by an Ostwald ripening scenario up to 1–2 nm due to the dominant role of thermal diffusion. Misfit dislocations sustain the existence of Nb-enriched domains of mixed symmetry. It is shown that growing dislocation loops and dissolving/growing precipitates result in the hardening change up to 0.01% at a dose rate of 10−5dpa/s and temperatures of 550–575 K. Obtained theoretical results are verified by experimental data.