Thermodynamics of Irradiation-Driven Phase Transformations in Zr-Nb Alloys

This study investigates the influence of supersaturated self-interstitial atoms (SIAs) on the thermodynamic stability of the Zr–Nb binary system. Utilizing a CALPHAD-based driven free energy model, we demonstrate that the significant negative eigenstrain of β precipitates is accommodated by SIA annihilation, which acts as a precipitation driving force for β . We compare Vegard’s law against a non-linear lattice model. While both models predict a decrease of the monotectoid temperature, the stabilization of β -Zr at low temperatures, and a reduction in Nb solubility limits, the non-linear model reveals a substantial distortion of the β -Nb boundary. Specifically, at high SIA supersaturations, the β -Nb and β -Zr stability domains tend to merge, providing a thermodynamic basis for the anomalous compositions observed in reactor environments. Finally, we discuss the potential impact of this radiation-induced β -Nb precipitation on both corrosion resistance and overall microstructural evolution.