Experimental investigation and thermodynamic re-assessment of the Mn-Gd binary system

In this work, 13 Mn-Gd alloys prepared by arc-melting method were investigated experimentally by means of differential thermal analysis. The temperatures of the invariant reactions and liquidus in the Mn-Gd binary system were determined according to the measured thermal analysis curves. One key as-cast Mn70Gd30 alloy was examined using differential thermal analysis and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy to confirm the type of the invariant reaction (L + Mn23Gd6 a dagger" Mn2Gd). Based on the critical review of the available experimental data measured in the present work and in the reported literature, the Mn-Gd binary system was assessed thermodynamically using the CALPHAD method. The solid solution phases including liquid, alpha-Mn, beta-Mn, gamma-Mn, delta-Mn, alpha-Gd and beta-Gd are modeled by the substitutional solution model, while the intermetallic compounds such as GdMn2, Gd6Mn23 and GdMn12 are treated as the stoichiometric compounds. A set of self-consistent thermodynamic parameters obtained finally to describe the Gibbs energies of various phases in the Mn-Gd binary system can be used to reproduce well phase equilibria and thermodynamic data.