Experimental Investigation and Thermodynamic Modeling of Phase Equilibria in the Hf-Ti-Si System

ABSTRACTPhase 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).

Processing and Characterizing RuAl Eutectics

ABSTRACTEutectic alloys in the Ru-Al-Mo system were directionally solidified by a cold crucible Czochralski technique. The solidification microstructures and composition of the phases were examined and used to estimate a partial liquidus projection. Preliminary results from compression and hardness testing indicate that the hardness of RuAl varies significantly with composition. The Ru-rich alloys in which RuAl is in equilibrium with the hcp (Ru,Mo) solid solution were found to have the lowest hardness values.