Construction of the Al–Ni–Si phase diagram over the whole composition and temperature ranges: thermodynamic modeling supported by key experiments and first-principles calculations

An extensive thermodynamic investigation of the Al – Ni – Si system is carried out via an integrated approach of calculation of phase diagrams, first-principles calculations, and key experiments. Eighteen decisive alloys are prepared in order to verify the existence of the previously reported ternary compounds and to provide new phase equilibrium data. Phase compositions, microstructure, and phase transition temperatures are determined using the combined techniques of X-ray diffraction, scanning electron microscopy, energy dispersion X-ray analysis, and differential thermal analysis. The order/disorder transition between disordered bcc_A2 and ordered bcc_B2 phases as well as that between disordered fcc_A1 and ordered L1 2 phase are described using a two-sublattice model. A self-consistent parameter set is finally obtained by considering the huge amount of experimental data including 13 vertical sections and 5 isothermal sections from both the literature and the present experiments. Almost all of the reliable phase diagram data can be well described by the present modeling. The reliability of the calculated thermodynamic properties for ternary phases is verified through enthalpy measurement employing drop calorimetry and first-principles calculations. The thermodynamic parameters obtained can also successfully predict most of the thermodynamic properties and describe the solidification path for the selected as-cast alloy Al 6 Ni 55 Si 39 .