Phase Equilibria of the Fe-Mo-Ta Ternary System

The phase equilibria of the Fe-Mo-Ta ternary system at 800 and 1000 °C have been experimentally investigated. The various phases in the alloys after annealing at 800 °C for 60 days and 1000 °C for 45 days were examined using scanning electron microscopy, energy-dispersive x-ray spectroscopy and x-ray diffraction. Two three-phase regions were confirmed at 800 °C and two three-phase fields at 1000 °C. No ternary phase was observed in any of the alloys. The experimental results indicated that the solubility of Mo in the Fe 7 Ta 6 phase and that of Ta in the Fe 7 Mo 6 are large. The solubility of Mo in Fe 7 Ta 6 is 16.5 at.% at 800 °C and 19.2 at.% at 1000 °C. In contrast, the solubility of Ta in Fe 7 Mo 6 is 29.3 at.% at 800 °C and 15.7 at.% at 1000 °C. In addition, Fe 2 Ta and Fe 2 Mo can combine as a continuous solid solution, denoted as Fe 2 (Mo, Ta), in the 800 °C isothermal section.