Influence of the initial composition on the phase equilibria in the case of the solid phase separation in binary alloy nanoparticles (exemplifying on the W-Cr system)

Abstract

Due to a unique set of physico-chemical properties, nanoparticle-fabricated heavy tungsten pseudo-alloys with the ultrafine-grained structure have become an object of a strong interest among researchers in the case of the up-to-date additive powder metallurgy technologies. In this paper, the peculiarities of the phase composition have been simulated in the framework of a thermodynamic approach to core-shell nanoparticles of a stratifying sold solution using the heavy W-Cr pseudo-alloy as an example. For a two-component system with the phase separation in the solid state, a specific effect has been demonstrated which consists in the fact that, unlike system in the macroscopic state, it is not only the volume fraction of co-existing phases but also their equilibrium composition varies depending on the initial composition of a the system. For two different heterogeneous states of a core-shell structure, the thermal stability areas have been obtained along with temperature-dependent equilibrium phase compositions of the system in each state. A thermodynamic interpretation of the obtained results has been described based on three possible mechanisms of reducing the free energy of the system.

Keywords

• nanoparticles
• phase separation
• chemical thermodynamics
• solubility
• core-shell
• tungsten
• chromium