Thermodynamic analysis of the Al-Si-Zr ternary system

A thermodynamic analysis of the Al-Si-Zr system has been performed using the CALPHAD technique. To enable a thermodynamic description of the binary systems, the results from a previous evaluation were adopted for the Al-Si and Si-Zr systems. Thermodynamic assessment of the Al-Zr binary system has been carried out previously; however, some experimental data on a stable compound and thermodynamic properties were not well reproduced by the optimized parameters. Thus, the thermodynamic analysis of this binary system was performed based on the experimental information for the phase boundaries and invariant reactions. To overcome the lack of experimental information on thermodynamic properties for this binary system, a first-principles method was applied to evaluate the enthalpies of formation of binary compounds. Variations in the enthalpies of formation for the ternary phases, (Al1-xSix)(3) Zr (I4/mmm) and (AlxSi1-x)Zr (Cmcm), with dissolving Si were also evaluated for superstructures constructed by modifying the stack of atoms along a given direction of the parent lattice structures. A thermodynamic assessment of the ternary system was performed based on the experimental information, as well as these first-principles data. The evaluated parameters reasonably reproduced most of the experimental data on the isothermal sections; however, discrepancies still exist in the location of some complex three-phase mixtures of intermetallics, and further investigation is required from both the experimental and thermodynamic points of view.