Thermodynamic assessment of the RE–Zn (RE = Dy, Er, Ho, Tb) binaries as a starting step for a Mg–Zn–Zr–Rare earth multicomponent database

Abstract

The study of Mg alloys containing Zn and Rare Earth (RE) elements is extremely important for several applications, such as bioimplants, due to their excellent biocompatibility and biocorrosion properties. Despite this fact, RE–Zn binary phase diagrams are not very well known, even though they are very similar to each other, being composed of several intermetallic compounds, usually concentrated near the Zn-rich side. In the present work, we propose a new thermodynamic assessment of four important RE–Zn (RE = Dy, Er, Ho, Tb) binary systems, following the CALPHAD method, as a launching board to the thermodynamic description of the Mg–Zn–Zr–RE multicomponent system. The liquid and bcc phases were described as substitutional solutions and all solid compounds were described as stoichiometric phases, thus avoiding models not easily extended to multicomponent systems and lacking implementation in widespread thermodynamic software. The resulting phase diagrams agree remarkably well with the available experimental data, making them ready to be incorporated into larger databases.