A new approach to construct bulk and size-dependent continuous binary solution phase diagrams of alloys

Abstract

The construction of bulk and size-dependent temperature–composition phase diagrams of alloys is critical for their industrial applications. However, the nano-phase diagrams are difficult to be determined accurately by experiments since the nano-phase equilibrium is metastable. In this work, a new approach was developed to construct both bulk and size-dependent continuous binary solution phase diagrams with three steps: (1) determining bulk atomic interaction energy by using ab initio molecular dynamics simulation; (2) calculating size-dependent melting enthalpy, melting temperature, and atomic interaction energy using a unified nanothermodynamics model; and (3) constructing phase diagrams with the above parameters, where a typical Au–Ag alloy was studied here as an example. It is found that (i) the simulated bulk atomic interaction energy is consistent with experimental data; (ii) the melting enthalpy, melting temperature, and atomic interaction energy decrease with decreasing material size for isolated nanocrystals; and (iii) the temperatures of the solidus and liquidus curves drop and the two-phase zone becomes small for the Au–Ag nanoalloy. The general approach developed here can be used to investigate other continuous binary alloy systems and can be extended to construct other phase diagrams, for example, the eutectic phase diagram.