Experimental Investigation and Thermodynamic Modelling of the Fe-Ni-Ta System

The liquidus surface projection and isothermal sections at 1200 and 1000 °C of the Fe-Ni-Ta system were established by Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectrometry (EDS) and x-ray diffraction (XRD). Eight primary solidification regions in the liquidus surface projection were experimentally obtained. The similar phase relations were derived in the isothermal sections at 1200 and 1000 °C. Based on the experimental results in the present work and reported in the literature, the Fe-Ni-Ta system was optimized by means of CALPHAD (CALculation of PHAse Diagram) method. Solution phases (liquid, fcc, bcc) were treated as the substitutional solution. The compounds Fe 2 Ta, Ni 2 Ta, Ni 3 Ta and NiTa 2 were treated as (Fe,Ni,Ta) m (Fe,Ni,Ta) n by a two-sublattice model, and (Fe,Ni) 7 Ta 6 was modelled as (Fe,Ni,Ta) 1 (Ta) 4 (Fe,Ni,Ta) 2 (Fe,Ni,Ta) 6 by a four-sublattice model. A set of self-consistent thermodynamic parameters for the Fe-Ni-Ta system was acquired.