Free energy diagram and spontaneous vitrification of an ion mixed metastable hexagonal phase in the NiMo system

Abstract

In the NiMo system, a metastable crystalline (MX) phase was formed by ion mixing and identified to have a hexagonal structure with a stoichiometry around Ni 75Mo 25. The MX phase transformed later into an amorphous state upon room temperature aging for 5 weeks. The observed spontaneous vitrification of the MX phase can be explained by our calculated free energy diagram, including free energy curves of the solid solution, the amorphous phase, the equilibrium compound and, for the first time, the ion mixed phase. The enthalpy of the MX phase was computed by considering the identified structural characteristics and the ferromagnetic effect contributed by nickel atoms.