Isothermal section at 1100 °C of the Fe–Ni–Ta system

The isothermal section of the Fe–Ni–Ta system at 1100 °C was constructed using 6 diffusion couples and 10 alloys, the compositions of which were selected on the basis of the experimental results of the (Fe–Ni alloy)/Ta diffusion couples. The samples were examined by means of optical microscopy, scanning electron microscopy, and electron probe microanalysis. Experimental results showed no existence of ternary compounds at 1100 °C. The following five three-phase equilibria were observed: (1) (Ta) + Ta2Ni + Ta(Fe, Ni), (2) Fe2Ta + Ta (Fe, Ni) + TaNi2, (3) Fe2Ta + TaNi2 + TaNi3, (4) Fe2Ta + TaNi3 + (Fe, Ni), (5) TaNi3 + TaNi8 + (Fe, Ni). The compounds FeTa and NiTa formed continuous solid solution. The solubility of Fe in TaNi2 and TaNi3 was determined to be 18 and 7.8 at.%, respectively, while the solubility of Ni in Fe2Ta was estimated to be 40 at.%.