Thermodynamic remodeling of the Al-Pt system towards an assessment of the Al-Ni-Pt system

The thermodynamic CALPHAD description of the Al-Pt system is remodeled. The four sub-lattice (4SL) model for the ordered/disordered fcc and bcc phases is adopted resulting in improved agreement with experiment and first-principles information compared to previous descriptions. First-principles calculations are performed and the results are used in addition to available experimental data as input for the modeling. Modeling results agree well with most experimental phase equilibria and thermochemical data compiled. Special attention is also paid to the metastable phase diagrams to ensure that the parameters obtained in the modeling do not present unphysical results in the metastable regime. The obtained fcc and bcc descriptions are converted to two sublattice (2SL) models to enable combination with available multi-component Ni-base superalloy descriptions. The converted Al-Pt system is extended into the Al-Ni-Pt ternary system to study its extrapolation characteristics using available thermodynamic and thermochemical data. It is found that the 2SL model is not adequate in capturing the thermodynamic behavior of the fcc-based phases found in the ternary Al-Ni-Pt system. Possible approaches for future work is discussed.