Precipitation of the Secondary Phase in Commercial Zirconium Alloys at Neutron Irradiation

Abstract

The work deals with the study of secondary-phase precipitation in binary and ternary zirconium-based alloys with extra-small content of doping within the framework of the phase-field approach. Developed phase-field model is applied to study β-phase precipitation in the model system of commercial Zr–Nb–Sn and Zr–Nb alloys at thermal treatment. An analysis of local rearrangement of doping and equilibrium vacancies during precipitation is provided. Kinetics of precipitation, size and distribution of the precipitates, concentration of the species in precipitates and matrix are studied. Mechanical response including the plastic deformations in precipitated solid is discussed. As shown, the yield-strength change increases during precipitation. Yield and ultimate strength are studied at different shear rates for the annealed alloy. Formation and growth of slip planes and dislocation loop–precipitate interaction governed by elastic-moduli difference is analysed. As shown, the emergence of dislocation loops around precipitates follows the Orowan’s mechanism. Modelling the radiation-induced precipitation during neutron irradiation of zirconium alloys with low content of doping is performed within the framework of the developed phase-field model by taking into account ballistic mixing and the dynamics of point defects with their sinks. As shown, in a sample initially containing precipitates of the secondary phase, irradiation results in the dissolution of precipitates at small doses and reprecipitation with dose accumulation. Analysis of precipitation dynamics and statistical distributions of precipitates with local rearrangement of non-equilibrium vacancies around precipitates at neutron irradiation is provided. As shown, the competition between the ballistic mixing and the thermodynamic force plays a major role in kinetics of radiation-induced precipitation and precipitates’ dissolution. The estimation of mechanical properties of Zr–Nb alloy during irradiation under reactor conditions is provided.

Keywords

• phase field
• precipitation
• neutron irradiation
• defects
• hardening