PHASE-EQUILIBRIA IN THE NI-AL-TA SYSTEM

Phase equilibria in the Ni-Al-Ta system were determined at 1000 and 12 50 degrees C. From metallography, X-ray diffraction and electron probe microanalysis (EPMA). two isothermal sections for Ta contents < 50 at . % were set up. The stability ranges of the Laves phase NiAlTa and th e Heusler phase Ni2AlTa were fixed and that of Ni6AlTa is confirmed. S everal other ternary intermetallic phases, which had been reported in the literature, are not confirmed. Lattice constants are given for all phases studied. For those phases with a large solid solubility range, i.e. NiTa and NiAlTa, they are given as a function of composition.