A thermodynamic description of the Gd-Mg-Y system

Thermodynamic modeling and optimization of the Gd-Mg, Mg-Y, Gd-Y binary systems and the Gd-Mg-Y ternary system have been critically carried out by means of the CALPHAD (CALculation of PHAse Diagrams) technique. The solution phases (liquid, body-centered cubic, and hexagonal close-packed) are modeled with the Redlich-Kister equation. The Compound Energy Model has been used to describe the thermodynamic functions of the intermetallic compounds in these systems. The compounds Mg2Y, Mg5Gd, Mg3Gd, Mg2Gd and Mg24Y5 in the Gd-Mg-Y system have been treated as the formulae (Mg, Y)2(Gd, Mg, Y), Mg5(Gd, Y), Mg3(Gd, Y), Mg2(Gd, Y) and Mg24(Gd, Mg, Y)4Y, respectively. A model (Gd, Mg, Y)0.5(Gd, Mg, Y)0.5 has been applied to describe the compound MgM formed by MgGd and MgY in order to cope with the order-disorder transition between the body-centered cubic solution (A2) and MgM with CsCl-type structure (B2) in the Gd-Mg-Y system. A set of self-consistent thermodynamic descriptions of the Gd-Mg-Y system have been obtained. The projection of the liquidus surfaces and the entire reaction schemes for the Gd-Mg-Y system have been constructed.