A thermodynamic description of the Mg–Pr–Y system

The thermodynamic modeling and optimization of the Mg–Pr, Pr–Y binary systems and Mg–Pr–Y ternary system were critically carried out by means of the CALPHAD (CALculation of PHAse Diagram) technique. The solution phases (liquid, body-centered cubic, hexagonal close-packed and double hexagonal close-packed) were 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,Mg12Pr,Mg41Pr5,Mg3Pr,Mg2Pr,Mg5M and Mg24Y 5 in the Mg–Pr–Y system were treated as the formulae (Mg,Y )2(Mg,Pr,Y ), Mg12(Pr,Y ),Mg41(Pr,Y )5,Mg3(Mg,Pr,Y ),Mg2(Pr,Y ),Mg5(Pr,Y ) and Mg24(Mg,Pr,Y )4Y, respectively. A two-sublattice model (Mg,Pr,Y )0.5(Mg,Pr,Y )0.5 was applied to describe the compound MgM formed by MgPr and MgY in order to cope with the order–disorder transition between body-centered cubic solution (A2) and MgM with CsCl-type structure (B2) in the Mg–Pr–Y system. A set of self-consistent thermodynamic descriptions of the Mg–Pr–Y system was obtained. The projection of the liquidus surfaces for the Mg–Pr–Y system and the complete reaction scheme for the Mg–Pr–Y system were predicted.