Thermodynamic optimization of the Ru–Sc system

The Ru–Sc system has been critically assessed by means of the CALculation of PHAse Diagram (CALPHAD) technique. The solution phases (liquid, body-centered cubic (bcc) and hexagonal close-packed(hcp)) were modeled with the Redlich–Kister equation. The intermetallic compounds Ru3Sc5, RuSc2, Ru4Sc11, Ru13Sc57 and Ru7Sc44 were treated as stoichiometric. The compound Ru2Sc, which has a homogeneity range, was modeled using two sublattices (Ru,Sc)2Sc. A two-sublattice model (Ru,Sc)0.5(Ru,Sc)0.5 was applied to describe the intermediate B2 compound RuSc with CsCl-type structure in order to cope with the order–disorder transition in the Ru–Sc system. Using this model, the ordered B2 compound RuSc and the disordered Sc-rich solution bcc are described by a single Gibbs energy function. A set of self-consistent thermodynamic parameters of the Ru–Sc system was obtained.