Thermodynamic modelling of the Hf–Pt system

Abstract

By means of the CALPHAD (CAlcultion of PHAse Diagram) technique, the Hf–Pt system was critically assessed. Based on the experimental data, the four solution phases (liquid, fcc, bcc and hcp) were described with the substitutional solution model. The intermetallic compounds Hf ₃Pt ₄ and αHfPt were treated as the formula (Hf,Pt) _m (Hf,Pt) _n by a two-sublattice model. Based on the solid solution range, the intermetallic compounds HfPt ₄ and Hf ₂Pt were treated as the formula (Hf,Pt) ₁(Pt) ₃ and (Hf) ₂(Hf,Pt) ₁, respectively. The intermetallic compound Hf ₂Pt ₃ was treated as a stoichiometric compound. The formulas (Hf,Pt) _0.5(Hf,Pt) _0.5 · (Va) ₃ and (Hf,Pt) _0.25(Hf,Pt) _0.75(Va) _0.5 were applied to describe the compounds βHfPt with CsCl-type structure (B2) and HfPt ₃ with Ni ₃Ti-type structure (D0 ₂₄) to cope with the order-disorder transition from bcc-A2 to bcc-B2 and hcp-A3 to hcp-D0 ₂₄. A set of self-consistent thermodynamic parameters of the Hf–Pt system was obtained.