Experimental Determination of Phase Equilibria in the Ni–Hf–Ta System at 950 °C and 1100 °C

The phase relationships at 950 °C and 1100 °C in the whole composition range of the Ni–Hf–Ta system were critically investigated using equilibrated alloys by scanning electron microscopy with energy dispersive spectrometry, and X-ray diffraction techniques. A ternary phase τ with Hf2Rh-structure was found in the annealed alloys, and the composition ranges of Ta were measured to be ~ 8.2 to 20.1 at. pct at 950 °C and ~ 7.1 to 20.7 at. pct at 1100 °C. The solid solubilities of Ta in the Ni–Hf binary compounds and Hf in the Ni–Ta binary compounds were determined. Two entire isothermal sections at 950 °C and 1100 °C in the Ni–Hf–Ta system were constructed, and 15 and 16 three-phase regions were determined, respectively.