Experimental investigation and thermodynamic modeling of phase equilibria in the Hf-Ti-Si system

Phase equilibria in ternary Hf-Ti-Si alloys were studied in the as-solidified and heat treated conditions using scanning electron microscopy, x-ray diffraction, and electron beam microprobe analysis. Selected solid-solid phase equilibria at 1350°C and a partial liquidus projection of the Hf-Ti-Si system at the metal rich end of the phase diagram were established. These data were then used to develop a thermodynamic description of the Hf-Ti-Si system using the CALPHAD (CALculation of PHAse Diagram) approach. The calculated isothermal section at 1350°C and the liquidus projection can satisfactorily account for the available experimental phase equilibria data and solidification paths. Both the calculations and the experimental data suggested that the metal-rich end of the ternary phase diagram possesses one transition reaction: L + (Hf,Ti)₅Si₃ → Hf(Ti)₂Si + β(Hf,Ti,Si).