Metastable phase nucleation in irradiated metallic alloys

Abstract

Phase nucleation in irradiated metallic alloys is studied by the atomistic Segregation-Charge Transfer (SCT) model, taking into account that when bombardment conditions favour the development of dense collision cascades the system explores kinetic and thermodynamic regions conventionally not accessible. Locally non-equilibrium compositional and charge density profiles evolve at the interface between a cascade and the crystalline matrix, driven by the interface enrichment of one of the film constituents. Charge relaxation to (meta)stable equilibrium is simulated by Charge Transfer Reactions (CTR), each involving a couple of dissimilar atoms of the initial alloy. Both the amount of energy needed in a single CTR and the local strain undergone by the target as a consequence of ion formation are calculated. Considering a set of nineteen alloys which are reported to be amorphized and seventeen ones which remain crystalline under ion bombardment, for both structure stability parameters threshold values are found, which allow to separate crystalline from vitrified alloys.